Sometimes you can crawl underneath and access the fill hole from below. If you do have to jack the bed up, by all means be careful and be safe! I believe there is another thread here about blocking up a bed.
Also , if the bed is raised up, a good idea after filling it is to leave the cap off the first time you let the bed back down. That way if you've overfilled it the excess fluid can get out and you won't blow the seals out of your hoist.
