Hooray! Was just about to suggest giving the 5V testpad attempt a go, but refreshed page and noticed that you've, wisely, did it already. I'm glad that you got it working, now you "only" need to cram all those cables inside N900's case in some meaningful way. You've, probably, found a way to do it already, but in case you don't - cutting off parts of the black plastic beneath microSD secondary board gives lot of space to run cables through there (you just need to fix secondary board in place via some other means).

BTW, I wonder what the hell happened, that regular path got broken somehow? Maybe micro-path inside multi-layer PCB got burned to crisps during initial soldering?

/Estel