Since you do have to claim your bag upon arrival at SJC, you might well have the opportunity to store it regardless of whether you have to check it through to LAS or not. Just take it through customs, after which they will take the bag back from you; you then reclaim at the regular baggage carouse and can just store it (if there are facilities) rather than re-checking it.
Note: I don't know if that would trigger any kind of security alert, though. Wouldn't make sense, but . . .
Note2: I've never connected through SJC, but I'm assuming that the baggage procedures are the same for connecting as well as SJC-bound passengers.
Note3: If you give the baggage folks your bag after clearing customs, you could probably fly to LAS and back by the time they get it to the regular baggage claim.
[This message has been edited by JHunter (edited 10-20-2002).]