Whats wrong with this then ?
The trouble was that Sprite could actually be a great many different objects, so I couldn't reference them collectively that way. However, your proposal got me looking over things again, and I realized that I'd been a total idiot! The nickname plugin offers exactly the condition that I needed:
Voila! All I needed was to have all possible sprites in a family (which they already were) and then use the nickname picker (that I somehow overlooked like five times yesterday) to select it.
Thanks so much for your help! This will save me a great deal of effort.