Thank you for posting in the RA2/Yr forum, Deezire, It's been awhile.
Deezire's method was to make the mechanic be an shp vehicle, like the Wolverine in TS. The only way to get a mechanic is to build a Service Depot, which gives you the mechanic as a free unit.
I think Renegade's suggestion would work...I've heard it before, but I'm terrible with particle systems, so I've never tested it.
If you put damage ( or negative damage, presumably ) on the animations from a particle system, it can kill things, but the kill will not count for the team, because the animation cannot be owned by a side.