In my opinion its not really worth it to even try and install FCS2 on a MacBook Air. Sure you could access any CD/DVD media via remote disk from the other computer, but once you get it on the Air you open up a whole other can of problems.
The MacBook Air is NOT built for video. The processor speeds are low, the system drive is small (FCS2 takes up something like 50-60GB of space).
But the biggest reason is that there is NO firewire on the MacBook Air. Yes there is USB, but USB just does not cut it for video, it simply cannot sustain constant data rates like firewire can and this can cause all sorts of problems when editing.
In my opinion upgrading the ram on your MBP is your best option. Any MBP is going to handle video better then a MacBook Air.
Ram is fairly cheep check out crucial.com
There are no “technical solutions” to your “artistic problems”.
Don’t let technology get in the way of your creativity!