This may not be as simple... or inexpensive as you might hope.
You might search and post the question to http://www.architosh.com/ . Mac-based architectural folks have to deal with file conversion issues fairly frequently.
Otherwise, you might consider getting a plug-in for your client's Solidworks app that allows it to export more universal formats. I know there's one for .obj format, but I have no personal experience with Solidworks.
Also on the PC side, Polytrans might work, but it's costly.
Hope this helps a little. If you do find a solution, let us know. I'm curious.