: I've heard of this method for years but I have a hard time
: believing even the thinnest resin will move through the fattest
: horse needle...

So try a thought experiment - would you have trepidation of taking a THIN horse needle and stabbing the bottom of a full container of that thin or typical resin? What would likely happen?

Or lay down $0.49 for a medical syringe and maybe you could be a believer too. Most syringes come with some kind of tip, so you'd have a basic start.

When using fillers, larger needles (and a caulk gun technique) can be helpful - good size ones can be obtained from lee valley:
(but this is not for your application or techique required)
http://www.leevalley.com/en/wood/page.aspx?p=20003&cat=1,110,42967