well, if you don't want to purchase the snowboard tuning clamps (which
work great and attach to any table) you just need some kind of rubber
to hold things in place. It'll move a little, but I'd think if you do
it on top of some old tires or put a rubber mat over whatever surface
you use. If you use the chairs, as suggested, drape an upside down car
mat over each chair. The rubber should hold the board nice.

http://snowboards-for-sale.com/snowboard_tuning_bench/