Any good way to add a handicap in Dominion?
As an informal handicap, when I'm playing in a game like this I usually try to make myself take my 2nd strategy - instead of doing the most obvious thing on the board, I come up with something more oddball and see if I can make that work.

Another thing that's not a huge handicap but can help is letting the less experienced players choose the 10 Kingdom cards, so they can pick things that fit into their own comfortable strategies.

I use both these techniques when playing with my wife (she plays every few months while I play 3 times a week at lunch) and thought I still win a lot, she has more fun this way.