Detecting unit within range of trackable

I'm trying to get a mining system working for my map, and I thought I could try using trackables. Basically, I have a system set up in which is you put your mouse over a trackable that represents certain materials, certain special effects appear there, and if you click it give you some of that material. I can do that fine, but need a way to detect who is mining (this is a multiplayer map). As there isn't a way to get the player who activated the trackable, I though I might be able to find the owner of the unit nearest the trackable. My problem is, I don't know how to get units in range of trackable.

Could anyone help or is this futile?

make the tracable a varable x,y then you can use it to find who is closest from that but not driectly from the tracbale its self there is almost no tracable api there are only like 5 lines in common j .