hmm. I tried out all settings and theres no other possibility than deactivating wpa and wep and only secure the wlan with an macfilter :/
And there is a second problem with the mac-changing.

When you want to drive for a long time, the tablet may drain all the power and then when you charged it then the old mac is back and you can't open the app any more because you dont have internet

Somebody should find a way to crack the app :/

HM! And I thought about a second method. Why don't we create an app that just forwards the whole gps datastream and acts as a USB-GPS-Receiver for a program on pc (to use it with a laptop and software that is already cracked )
Hm.. cracking the wayfinder would be the more elegant way though.