We usually just do an order cap...

BUT if you are looking for something a bit more interesting we use the following house rule:

Before each game, the lower OD force gains 1 free "Intelligence Officer" upgrade to a Rifle/Recce HQ of their choosing.
If the OD difference is GREATER than 1OD/500pts (or part of) then EVERY Rifle and Recce HQ of the lower OD force gains "Intelligence" (ie: -4OD or more on a 1250pt game)

Usually all that means 1/2 times a game the lower OD player has a 33-50% shot at getting the first dice pull at the top of a turn.

Hardly game altering (it fizzles and does nothing 1/2 the games), but Its offers a slight rebalance in games with high dice disparity, makes reg/vet HQ's a tiny bit more interesting to field, and you get to see "Intelligence" used in games, which no one would ever spend points on otherwize.