I stumbled upon this over at armaholic.com
http://www.armaholic.com/page.php?id=797
Looks quite interesting, though havent tested it yet.
Loops calculating required velocity vectors after working out distance vectors to a given target point, then uses setVelocity (at least thats what I gather from reading through the scripts, I'm still not fully up to speed on syntax etc)
Will have to have a play with it... would still prefer control over waypoint activation radius but this may work around it in the short term...