The only way I can get my friends to play Dominion with me is if I replace one or two of my starting Coppers with Curses, to keep it interesting. As a result, they won't play with me online, where this is not possible. Would you consider implementing that option in unranked games?
What about just skipping the first X turns? If you really want curses involved you can say that you must buy a Curse on the first or second turn, or something of the like. :)
Another thing that we sometimes do is: before the game the handicapped player choses a protected pile. Then, their opponents agree on a pile (other than the protected one) that the handicapped player may not gain during the game.
It works very well for casual games, even though the degree of handicap is very kingdom-dependent.
The objective is to be able to play with them, and the only way to acheive that is protect their feelings. In a decade of experience in frequently recruiting new players to Dominion, one of my findings was that I have to use a handicap method that lets them distract themselves from the handicap so they can forget it. If they see me pass on several of the opening turns, it drives it home too much.
If I start with a weakened starting deck, then after the game, they take joy in their victory and want to play a second game-- unless a smartass with poor social skills points out that I started the game with four Curses, three Coppers, and three Estates. Then the enthusiasm for playing a second game immediately wanes. A good handicap method is one which politely crawls into a memory hole.