Have you tested that only the owner of a trap gets the xp?I don't have a modding solution for you, but here's a possible stopgap solution for your group--the trap "owner" is whoever places it, regardless of who crafts it or wires it up. So, if your friends place some traps, they can get xp from those (provided they're perked into that tree, which I realize isn't ideal).
I, too, would love to see a more equitable distribution of trap xp.