With the PICs I've been using, Vcc not RTN is nearest the oscilator pins. I
don't know if this is true the the whole PIC line, but may well be.

So when I have to ground my osc caps (actually I use a resonator, same
thing applies), I could either go the long way around to the real ground
pin, or "Ground" these caps to Vcc. Guess what I do? Nail em right to Vcc. 

Vcc is an AC short to ground (what do you think all those bypass caps do?),
and is a fine return point for the caps. My application is an accurate
timer, so I implicitly test start-up time. I've tested these things from
-60 to +150�C and they start up and start pronto every time.