Best I can come up with, is installing some sort of remote control program on the downstairs computer. Something like VNC. You could use this to stop the printer from processing documents, change the paper, then tell it to start up again.
That, or rig up some kind of a switch that will turn the printer off and on.
If you had a print server of some kind, you could probably access it via the network, and tell it to stop processing queue documents.
Otherwise, don't think of it as having to make two trips, think of it as exercise. Couple of trips up and down a flight of stairs will get the heart going, burn some calories, tone muscles, all that good stuff.
I've have a computer upstairs, networked via wifi to a downstairs printer. Sometimes I'd like to be able to change the paper in the printer before it prints - but that would mean going downstairs, changing the paper, then running back upstairs and clicking "print". Is there any way I can set the printer to wait a minute or so, to allow me time to change the paper? Thanks in advance for any suggestions.