I would do the exact opposite and buy boots(you can always return them after a day or two) and rent board/bindings.
Most mountains i've tried out here had trash boots that are either way too stiff, have zero padding, or are packed out from being ridden dozens if not hundreds of times.
But since hes a skier he can probably get away without renting, because hes probably in good enough shape to learn snowboarding without giving up.
Most people give up snowboarding because they are out of shape and get tired after an hour of falling.
Boots are by far your most important peice of equipment though, I would say moreso than your board.
You can snowboard with a shitty board/bindings and good boots just fine, you might not have the minut control you get with better bindings/boards but you can learn and get down the mountain.
If you try riding with shitty boots you will quit in an hour after your feet are numb or aching to hell or both.
'09 151 Never Summer SL-R
'10 K2 T1 DB Bots
'09 Burton Cartel Bindings