It's obviously an easy and good idea at the same time... but I am afraid the DEVs have more pressing matters.
Until something like that is developed, the best thing is the Tempe... personally, I would completely remove the internal thermometer but i really really hope they take your suggestion (we suggested that many times already... to no avail, though).
If you want to see the ambient temperature (or as close as possible), get a Tempe Sensor. The only thing that could be done calibration is to add some kind of a "bias" to the internal reading, but determining that bias isn't easy, as it's impacted by things like if you are wearing the watch, are you wearing long sleeves (which may insulate the watch), are you in the sun, etc.
And consider the times when the ambient temp is close to body temperature or above it (it was 119F a few days this summer for me!)
I use an #3 S-Biner clip with mine, and can easily clip it in the best place - pack strap, under the bike seat, etc.
If someone paypaled you $25 for a tempe sensor, would that make you happy? :) There is a reason the Tempe exists!
Do you have a picture showing us your set up with the #3 S clip biner and the Tempe? I am thinking about getting one of those for my Tempe so would be nice to see your set up...
Remove the temp sensor, or disable the ability for its data to be displayed? The temp sensor is required for calibration of the barometric sensor, FYI.
Like Jim, I use a Tempe and from his suggestion I'm also using the #3 S-Biner...great combo.
Do you have a picture showing us your set up with the #3 S clip biner and the Tempe? I am thinking about getting one of those for my Tempe so would be nice to see your set up...