On busy powder days at Whistler, I move up through the main lines as a single by jumping from groups of 2/3 to other groups of 2/3. I never bypass a group of 4 to do this, and I always ask politely if I can join a group. I have never had anyone give me attitude for this and I do it constantly. The singles lines at Whistler move slower than the main lines on busy days. Just be confident and look like you know what you're doing and no one will call you out.
To add, the following are lift line activities which deserve (and often get) heckling at Whistler:
1) Snowboarders (or more rarely, skiers) not doubling up for T-Bars on powder days, especially on Blackcomb. This is inexcusable but seems to be more accepted every year. Lifties should not be loading singles on busy powder days.
2) Ski school attempting to use the ski school line on powder days while people have been waiting for the chair to open. I think WB actually has a policy that ski school must wait 20 minutes (approx. the time it takes for all the queued skiers to load one chair cycle) before using it, with the reason being that paying guests getting pelted with snowballs/heckled out of line kind of ruins their day.