Hey, that sounds like a nifty idea. GSanc, then buff, then dispel the GSanc, and you're smack in the middle of a bunch of monsters, nigh-untouchable, with a few death-dealing megaspells at your fingertips.
I really hope my PnP PCs don't figure that one out.
As for a token to end GSanc, I believe I've heard of one, but you'd have to check with someone who knows Divine magic a bit better.