What
@into_the_t said, but maybe pull the ink cartridges out and stick a damp paper towel under the print head.
That seems like a not so good idea
That would leave the ports where the carts plug into the head open and subject to drying. Also, it would leave the bottom of the head exposed to drying--a paper towel, damp or not, is not going to keep the head moist for 3 weeks.
The printer keeps the head parked and sealed when not in use. Print something before you leave and do a nozzle check when you get back. If there are blocked nozzles, do a cleaning. If there are still blocked nozzles, let it sit for a few hours or even the next day and then do another nozzle check and cleaning, if needed.