I think openlimping small pairs in EP is acceptable at 50nl and below, and maybe even at 100nl.

At the stakes I play (100nl/200nl/400nl) I raise all pairs and cbet all heads up flops and it works for me.

If you open limp and miss your set with 22-66 your best be is to check/fold. You didn't raise PF so you don't have much postflop credibility. Remember you aren't betting the flop because you have a pair, you are betting it to represent top pair or overpair. Your pair is just backup in case he calls with a draw.