Originally Posted by JB99Disco

Went with a small rope around the heater pipe, pulling (hard) and tightening clamp at the same time. Once it gets in there the clamp is easy to tighten. Thanks for the info, looks like I am leak free and yes Heater Matrix replacement lived up to its nasty reputation.

Rubber hose thread above looks like a good option too, just couldn't bring myself to take off the dash again.