It probably isn't necessary to hack the cab, the manafest file tells you what to rename in the cab and where to put it, plus a couple of registry entries. The only thing that gets skipped is a import to funsetup.dll which at a glance is registering MIME types.
<wap-provisioningdoc>
<characteristic type="Install">
<parm name="InstallPhase" value="install" />
<parm name="SetupDLL" value="1" />
<parm name="BuildNumberMin" value="0" />
<parm name="BuildNumberMax" value="-536870912" />
<parm name="AppName" value="Funambol Sync" />
<parm name="InstallDir" value="%CE1%\Funambol" translation="install" />
<parm name="NumDirs" value="3" />
<parm name="NumFiles" value="11" />
<parm name="NumRegKeys" value="4" />
<parm name="NumRegVals" value="9" />
<parm name="NumShortcuts" value="1" />
</characteristic>
<characteristic type="FileOperation">
<characteristic type="%InstallDir%" translation="install">
<characteristic type="MakeDir" />
<characteristic type="Funambol.exe" translation="install">
<characteristic type="Extract">
<parm name="Source" value="Funambol.001" />
</characteristic>
</characteristic>
<characteristic type="startsync.exe" translation="install">
<characteristic type="Extract">
<parm name="Source" value="STARTS~1.002" />
</characteristic>
</characteristic>
<characteristic type="LICENSE.txt" translation="install">
<characteristic type="Extract">
<parm name="Source" value="0LICENSE.003" />
</characteristic>
</characteristic>
<characteristic type="handleservice.exe" translation="install">
<characteristic type="Extract">
<parm name="Source" value="HANDLE~1.004" />
</characteristic>
</characteristic>
<characteristic type="language-en.dll" translation="install">
<characteristic type="Extract">
<parm name="Source" value="LANGUA~1.005" />
</characteristic>
</characteristic>
<characteristic type="language-de.dll" translation="install">
<characteristic type="Extract">
<parm name="Source" value="LANGUA~2.006" />
</characteristic>
</characteristic>
<characteristic type="ClientPush.exe" translation="install">
<characteristic type="Extract">
<parm name="Source" value="CLIENT~1.007" />
</characteristic>
</characteristic>
</characteristic>
<characteristic type="%CE2%" translation="install">
<characteristic type="MakeDir" />
<characteristic type="mainclientdll.dll" translation="install">
<characteristic type="Extract">
<parm name="Source" value="MAINCL~1.008" />
</characteristic>
</characteristic>
<characteristic type="funsetup.dll" translation="install">
<characteristic type="Extract">
<parm name="Source" value="funsetup.009" />
</characteristic>
</characteristic>
<characteristic type="syncmltransport.dll" translation="install">
<characteristic type="Extract">
<parm name="Source" value="SYNCML~1.010" />
</characteristic>
</characteristic>
<characteristic type="notlstnr.dll" translation="install">
<characteristic type="Extract">
<parm name="Source" value="notlstnr.011" />
</characteristic>
</characteristic>
</characteristic>
<characteristic type="%CE11%" translation="install">
<characteristic type="MakeDir" />
<characteristic type="Funambol.lnk" translation="install">
<characteristic type="Shortcut">
<parm name="Source" value="%InstallDir%\Funambol.exe" translation="install" />
</characteristic>
</characteristic>
</characteristic>
</characteristic>
<characteristic type="Registry">
<characteristic type="HKLM\Software\Funambol\SyncclientPIM\spds\syncml\Conn">
<parm name="userAgent" value="Funambol Pocket PC Sync Client 9.0.2" datatype="string" />
</characteristic>
<characteristic type="HKLM\Software\Funambol\SyncclientPIM\spds\syncml\DevDetail">
<parm name="swv" value="9.0.2" datatype="string" />
<parm name="oem" value="9.0.2" datatype="string" />
</characteristic>
<characteristic type="HKLM\Software\Funambol\SyncclientPIM\brand">
<parm name="showUrlField" value="1" datatype="string" />
<parm name="showAdvSettingMenu" value="1" datatype="string" />
<parm name="showSourcesSettings" value="1" datatype="string" />
<parm name="sourceOrder" value="mail,contact,calendar,task,note,picture,briefcase" datatype="string" />
</characteristic>
<characteristic type="HKLM\Software\Funambol\SyncclientPIM">
<parm name="path" value="%InstallDir%" datatype="string" translation="install" />
<parm name="pluginVersion" value="9.0.2" datatype="string" />
</characteristic>
</characteristic>
</wap-provisioningdoc>
%CE1% is \Program Files, %CE2% \Windows, the rest is fairly clear.