Ok, for all the geeks in the forum

- The basic idea is to tell the iPhone that the wifi connection does not access the internet;
- Everything lies in your ELM wifi settings on the iPhone;
- select your ELM OBD II device in the wifi list;
- tap the info button and choose the "STATIC" mode;
- enter IP address (from dongle user manual);
- enter sub-net mask (ditto);
- MAKE SURE NO ROUTER NUMBER IS ENTERED.
...et voilà! Done!
I can now use my GPS and Dashcmd at the same time