A lot of way of doing that, but i use this
http://www.stewmac.com/shop/Tools/Dr...uter_Base.html
I use a forum tool for many applications and this router style base for my hand set is really nice. very well made.
depends on the type of drill that you might use too.
the simplest way would be a pieces of hard wood with a flat bottom and a hole the same size as the bit. the hole being perpendicular to the bottom. the block gives you a wide stable base. cut the block down to size leaving you the extended depth of the bit that you need.