You're a good man.
I went through the same process as you just did, a week ago. I got it working quite alright, but decided to just go with the regular XBMC builds and use Spotimc instead... Took me a day or two before I quite understood what all that Git stuff was about - let alone finding the right branch and compiling it! What a lenghty process. I still have the SpotyXBMC2 (Frodo Alpha 1 based) 32-bit Windows install .exe if anyone wants it?
In part because of the exact same "problem" you're talking about here. Because it has to load all that album information and cover art for every artist in your library, it takes A LOT of time (in which XBMC just freezes) before it opens... And there's no clear way to tell whether it's an artist from Spotify or a local artist, and thus, you also easily end up with two duplicate artists in your library view (one for local, one for Spotify).
Plus, I found it to be slow and a bit unresponsive... But it's on the right track, still.
Get it integrated a bit better, perhaps by adding a "Spotify" submenu (next to your local Artists, Album, Genre etc. submenus) and have it work the same way, and I'd definitely be using it. Oh, and maybe start compiling builds as well, and just uploading the finished .exes.
I don't think what you're looking for is possible, the way SpotyXBMC2 works at the moment. But one can only hope they'll continue developing this otherwise excellent little gem.