: "just push both bits all the way in and tighten."

: A relatively minor point, but this is bad practice. You should not seat
: router bit shafts all the way to the bottom of the collet, but leave 1/16
: or so free. IIRC this is to allow for thermal expansion and possible
: galling. I doubt if this is a major source of damage, but it's a
: consideration.

This can be a serious safety issue -- by bottoming out the bits some collets won't properly secure the bit. They need to draw the bit down a smig as the collet cinches tightly around the shank. Flying bits are bad. I haven't tried it, but here's a variation of your idea; one thing I read said to put a rubber o-ring in the bottom of the collet (assuming your router is upside down on the table). This will register your height but still allow enough give for the collet to cinch the bit correctly.
Mark