As a general rule, if there's nowhere set-aside for the purpose, pull off to the side of the taxiway a short distance prior to the entering the runway and do it there.
As an absolute rule, if told to expedite before you have confirmed that the aircraft is fit for flight, refuse. If to remain on the runway would potentially cause an accident (which it certainly wouldn't have done here), go off the side of the runway - but that is still preferable to flying without having completed your pre-flight checks and engine run-ups.
"Unable to comply, conducting engine run-ups on the runway as you advised sir". Emphasis on the sir!
G