I don't think that Davet or I were suggesting that there weren't ways to manage the situation. If they have someone who is trained to play in the scrum then I would still then suggest that it is up to th non-infringing team to decide the numbers and format of the scrum.
However, first of all if they infringing team doesn't have a trained replacement on the field, then for safety reasons you can't force them to match numbers.
In terms of substituting a player due to the first being given a YC, Law 3.13 doesn't mention anything about players other than front row players, therefore you don't really have the option of requesting substiutions to provide a suitably trained 2nd or back rower, or at least as far as I can tell. Having 7 in the scrum is not a reason to go uncontested unless it's a front rower, in which case the law gives us the mandate to request a replacement. However it says nothing about any other position... again, I'd suggest that without a mandate you can't force it upon the coach...
If they request uncontested scrums due to the lack of a trained 2nd rower on the field due to YC, I can't see any option to force them to provide a replacement via temp sub, but I'm sure you could ask nicely?
This seems to be turning into a management question... both safety and game...