Unfortunately you need to be a Danish resident, or at least have a Danish bank account and mobile number as they are linked to each other. Setting up a Danish bank account wont work either as there are too many implications, basically needing to be resident in Denmark again. As it stands it seems the only way of getting home end tickets right now would be if you know somebody resident in Denmark.
I could be wrong, but card payments might possibly be accepted, not everyone in the older generation will be keen on the idea of mobilepay, and not everyone will be able to go out to the stadium for collection, this is just a guess though.
Brondby usually sell their tickets via Billeto.dk, I'd never used mobile pay when I was purchasing tickets, it was always just the standard using the card online, but this was with a Danish account, again issues could arise with British cards/Addresses attempting bulk purchases.
For the time being its pretty much just a case of waiting to see what happens come 5th October and if we can purchase online, failing that, its probably going to be who you know in Denmark.