I think you could do it using the technique outline here in the Android docs. (I'm now experimenting with it, but for different purposes). Basically, this lets devices broadcast and discover DNS-SD TXT records. As you'll see in the Android docs, you can load a Map object into one of these records and the receiving device can read it. It doesn't support a lot of bytes (I was trying to jam in an image converted to Base64 strings and that was way too much data), but it would support strings for latitude and longitude. Users would need to install your app on both sides for it to work, of course. Interactions can be passive until such time as you need to trade larger amounts of data, at which time a socket needs to be setup, etc., which requires the user to click to accept via a popup dialog.
If you copy/paste their sample code, it will pretty much get you going with something you can build on.