Using a half vial of Clarity Ferm

Possible?

The directions say its good for 5-7 gallons.  I brew 2.5 gallons.

Sanitize the vial, dump half in with sanitized hands, and recap with a sanitized cap.  Store at room temp in a ziploc ® bag.  Sound like a plan or a recipe for failure?

Might as well try.  Seems like it ought to be OK.