I hate selecting a mixed army, ordering "fight" and seeing the cloggers sit still.

It has been suggested to give Clogger a fake weapon to solve this. I recommend instead a widget that converts its fight commands to move commands. It would be trivial to make, more configurable, prevents the use of a fake weapon which could confuse other parts of the game, and best of all everyone loves more widgets.

First give a move command to group then fight command, and cloggers will keep moving.

Clicking a mixed army to fight sounds like a bad practice though

Im no expert of CA but there seems to be an extra unit behaviour that could be added at this point: Some kind of clogging lua magic that would behave like the fight command but upon an enemy getting into range it would issue movement orders towards said enemy.

make it throw a tiny amount of dirt as a projectile

Fake weapon is best imo, it could even use autoswarm and rush towards enemy units to block them.

Much better than widget. Also widget would break other things, including transport AI.

Maybe canfight=true in the the unit definition file is enough.