My local computer man gave me this idea to try.
An Inductive capacitative link.
Put some electrical tape around your mobile ,sticky side out with a couple of matches in there to give a little room. Wind about 20ft of insulated wire in a coil around that with tape between the layers if it goes multilayered. finnish off with a foot sticking up at the top and now put tape round the outside sticky side in .
Make it so it is removable is the way.
I picked up 1 bar on my USB modem that way