Is it possible perhaps to post on Facebook etc for anyone local to you with an ANT+ sensor (hr, tempe, foot pod etc) for you to go to them and do a quick test? If you were local to me, for example, I'd let you borrow my Tempe.
As a thought though they are £20 at the moment on eBay (so quite cheap), so depending on if you'd find use for an external Temperature sensor it may be worth the money just for the test.
Any local running groups to you on FB for example - someone there would probably have a ANT+ sensor?