Any way to boost bluetooth range

Now I know this is not a typical issue, but I was hoping some of you may have some solutions. I just purchased an iPhone 4 for my brother. He loves it, but the problem is he works in harsh environments (namely, on top of roofs in FL needless to say in sweltering heat). What he would like to be able to do is keep the phone in an airconditioned place like a car or home at a workshop where possible, and use a bluetooth headset for music and calls. Of course, this runs into the problem of range. I have looked, but I haven't been able to find any type of 'bluetooth signal booster' for something like an iphone (although there are apparenly such things for Macs and PCs with USB ports).

Anyone know of anything like that, or any other ideas for solutions?

BTW, he's got the toughest case we can find on the market yet and the film, but he's still not comfortable taking it with him on some jobs for obvious reasons.

Thanks!