As far as I'm aware, there's no way of forcing the update. There are a number of things that get checked for when it looks for the update, software number is one of them, along with what's called the CID (Stands for Carrier ID I
think). Unbranded handsets should have a CID of HTC_011 (or similar), if that doesn't match, the update won't install. Check your CID with
CID Getter.
That's your Android version, there should be a software version/number on the same page? if it's 2.2.1, it should be 1.72.405.x