I don't know if this is possible, but what about a tag in the Hopper to mark bill threads as having been Clarked? In the same way there is a "liked" tag, maybe the SS or the sponsor can hit it once the bill is in the digest. Is something like that possible?
Azul, sorry if I didn't answer to this, it's a very good suggestion (also for other areas than the Hopper, see Immigration where Eðo is manually tagging immigration threads depending on status).
I'm looking into it, unfortunately SMF's mod site seems to be having trouble.