There is a Merc solo that I don't see many use on their lists: Ragman.
I think this guy has potential with Khador, specially the Weaponmaster models and the Man-o-War Demo Corp. Death Field Demo Corps do 11 or so Damage each on average on the charge against ARM 19 (55 damage total, so they can one turn an unbuffed Stormwall). Great Bears can almost do similar numbers (9 damage on charge swing each, 5.5 damage on the second, totaling 43.5; not bad for a 5 point unit).
Can Gorman do this? Yeah, Rust Bomb can do a -2 ARM debuff. But both can work together and stack the Arm Debuff. I suspect using them both might be a solid 4 point investment against Colossals.