Leave it to the nitpickers to search for a way to be at 500.00 feet and not, heaven forbid 498.33 feet above the ground.
The rule is "not less than 500", the rule is not "precisely 500".
Try flying at 600 feet away, and if you are wrong, you have margin.
The altimeter is not more accurate than about 70 feet in any case, considering its own imprecision and inaccuracy. So if you set your altimeter to station pressure, and read 500 feet, you could be as close as 430 feet. Deal with it.