I modified the SharePoint Solution Installer and now it supports SharePoint 2010.
I added following config entry into the setup.exe.config
<add key=”SupportedSharePointVersion” value=”2007″/>
If it contains value “2007” then the solution can be installed only to MOSS 2007 and WSS 3.0
If it contains “2010” the the solution can be installed only to SharePoint 2010 and SharePoint Foundation.
If you leave it empty then no check for specific version of SP is done and you can install it to all above versions.
You can download the modified SSI binaries and source code from here. (It is actually a zip file renamed to jpeg because of WordPress policy.)