Hi,
I do that to my van's cooling system. I use an old funnel I made up with a
piece of aluminum fire suppression tubing.  The tubing fits into the hole
after you remove that pesky bleeder screw/bolt.  Mine comes out, but it is
tight quarters.  I put an "s-bend" into that appx 1/4" tubing and attached
that to a piece of hose, then out to the funnel...I 'top-up' the radiator
through the bleed hole and find it works great rather than all that fussing
around with throttle and engine speed and getting the van on the proper
slant, etc etc.
  I just park mine on a hill with the radiator high.  Let it sit a bit and
take out the bleed screw.  Pour in the coolant till it stops 'bubbling' and
comes back out as a steady stream..No more air at all in there.  I carry
that setup along in case I overheat along the road somewhere..hasn't
happened yet.
  Don Hanson