Is there a “help mechanic” in Macho Women With Guns?

Macho Women With Guns 2e uses a GURPS-like 3d6 roll-under resolution mechanic. We were playing it today and we happened into a scene where all the characters needed to cooperate on a group effort (the PCs were the Spice Girls and they were trying to do a karaoke performance to defeat an opponent).

I looked around and couldn’t find any sort of aid/group/help/collaborate/whatever mechanic to reflect when multiple Macho Women are attempting to cooperate on the same task. I ended up making everyone roll and just added up the points by which they made/didn’t make the roll but that had its problems – whenever the roll was hard or easy the sums “ran away” quickly in that direction over a lesser number of opponents.

An answer from a similar game like MWwG 1e would be fine; obviously the d20 Modern-based Mongoose edition has one but it’s not relevant or compatible. We couldn’t think of a mechanic for it in GURPS either or I would have just cribbed that.