My suggestion: you should be able to store a second Cumulus number to which you could then pass on advantage coupons or coupons from stamp cards in a simple way with one click...
I'll explain the issue using 2 case studies from the grandparents' generation to the parents' generation:

-- From many sides, the approach of radio plays via the stamp card was criticized: only the parents know which characters are coming up. How would it be if the coupons - or even better the individual stamps - could be transferred to a specific, stored Cumulus number?

-- Grandparents - but also other people - look after the grandchildren or entrusted children and it often happens that you buy something for the children (also on behalf of the parents) that you wouldn't have to do for your own use. The "advantage coupon generator" recognizes a potential customer and spits out a 20*, 40* and can't know that it was just a "purchase on behalf"...
and it's not the point of M-Cumulus to have subsequent purchases made by the "wrong people".

I'm afraid that the stamp card system is becoming more and more popular, especially for campaigns involving the parents' generation (stuffed animals, Mania, etc.), because this generation has smartphones 100% of the time. This way of giving points relieves the staff and also prevents cheating by the staff (from Migros' point of view ;-) )
Of course, it is at the discretion of M-Cumulus to determine which advantage coupons could be "inherited"...