My recommendation would be to keep searching and buy one already with the vacuum. If you think you might be going on occasional trips to "the sticks" where you may not have cell service or rapid roadside assistance then you can also buy the spare tire kit for around $300 and stick the spare in the stow-n-go bucket for long trips. The jack and lug wrench come with this kit.
However, member Redltd graciously provided us with a very nice DIY for removing the vacuum option to install the spare tire kit (the opposite of what you want). You would basically be doing the reverse but you will have more internal panels to immediately replace than Tony did and there may be some wiring issues if all the electrical cables aren't already installed. And, of course, you have to source the vacuum plus hoses and fittings, the on/off switch, internal front and rear trim panels and any associated mounting brackets, hardware, etc.
Look at the 5th post in this thread...
http://www.pacificaforums.com/forum/458-tires-wheels-suspension/2674-spare-tire-kit.html
