No this isn't a double exp trick, just an observation:
So playing Oddball with a buddy just now (this trick only works on larger maps with nooks/crannies, so no, not Haven). And it's the two of us kind of tucked in a corner, teammates are keeping enemies away. And we keep playing catch back and forth with the Ball. And every time you catch the ball, you get +5. So we just kept tossing it back and forth and back and forth.
No I didn't break the bank getting points, but I think I got an extra 100 while killing time in-game anyways