I played around here, and the Browser plugin kinda seems to solve the problem.
you can make an fullscreen request on an 'On Touch' block (unfortunately or not, browsers block any fullscreen request that's not associated to an user input) so then you set the audio property Timescale Audio to On.
So then you make:
Browser | Is fullscreen
>> System | Set Time Scale to 1
//any more pausing effects you may want (I used opacity and a pausing icon)
System | Else
>> System | Set Time Scale to 0
//remove pause effects
You can only hold X when you aren't in fullscreen mode.
And since the game (and audio) pause when aren't in fullscreen, you can't pause something that's already paused.