GSM Shield: Replacing the integrated antenna with an external one

I recently purchased the official Arduino GSM Shield and while it works great, I'm kicking myself for not purchasing the version that uses an external antenna. I ultimately want to build a weather balloon and I'm afraid that the integrated antenna will not be strong enough while enclosed inside a styrofoam container.

Does anyone have any experience in swapping out the integrated antenna with an external one? Any tips or things to keep in mind?

Thank you!

Styrofoam should pass the RF perfectly.

I seem to recall it being used (mainly for demonstration purposes) as microwave lenses.

I'm having the same problem-kind of -

Disconnected (cut off) built in antenna and connected an external one, but I'm not seeing any improvement in signal strength.

Well, if we could only see the workmanship of your kludge, we might have some explanation.