L6-30 Extension for UPS?

I have a L6-30R that is up in the ceiling of our new facility. It is roughly 10ft from the ground. It is also offset to the side of the rack by a foot or so. So the UPS unit I have only has a 10ft power cord.

Short of getting the electrician to lower and shift the receptacle closer to the rack, could I use a extension (say 3 to 6ft)? Like the ones shown HERE or HERE?

Thanks.