Setting terminator in Preferred Applications

Hi, first of all, congrats on the great job you guys are doing.

I'm not sure if this the right place to ask this but let's see if you can help me out:
I want Terminator to be started as my preferred terminal application and so I configured it at Gnome's Preferred Applications (System tab). However since I want it to start with -bm options I selected "Custom" and I completed the commands needed for this. The thing is that it does not work (it opens gnome-terminal) and when I open Preferred Applications again I see the normal gnome-terminal is back again as the default one. If I choose Terminal (no switchs possible) I get Terminal.

I guess you guys also have it as your preferred terminal application and so I need to know if you faced similar difficulties when trying to set it up and how you fix it (I think I can add the -b and -m switch in my .terminatorrc but I'm not sure which are the key words to use).

TIA
Mariano.