Like others have said, no your not supposed to. Can you make it an
outlet location versus a blank? That would be my preference if you cant
run an entire new wire.

I have burried a box once but it was the only way to do the project w/o
significant major headaches. Yea yea think of that guy trying to
troubleshoot something down the road and what a pain it would be. Sorry
if thats they guy reading this someday. I did use a box, a cover, wire
nuts and electrical tape. I suppose I could have also soldered and used
heat shrink tape for an even better connection but oh well. I don't
live there any more. Blank or outlet were not an option (It was under a
sub floor, under carpet)