'grouping' a single move and maintaining delegate_to (reconciliation)

We’re using grouping payments in order to deal with supplier exchange bill vouchers, but have the problem where every now and then we have exchange bills with only one invoice.
NB In the French plan, the counter part is always put in a special account (typical 403x) where the supplier invoices themselves are typically in the primary supplier account 4011x.

Currently grouping chokes on only one line.

So I tried to manually generate a move, but (I guess naturally) it is not possible to update the reconciliation of the primary account move line to delegate to the reconciliation of the special account move line.

In the end, it seems pertinent that if the counter part is put in a different account that single moves should be accepted.

So I’d like to see the feature added to modify (in the grouping popup) the counter part account and, while were at it, also specify the date of the move operation, since today() is probably only useful in 0,00000001% of accounting cases (if that).

The sticky problem with manual payments with compensations is that there seems not to be any delegate_to reconciliation set up either, so it doesn’t really work for ‘cash_basis’. Besides, the compensation account can’t seem to have party_required, which is the case for 403x not to mention that the journal must be a bank journal which isn’t the case either (prior to compensation, anyway).

The grouping wizard is not design for this purpose.
For check and bill of exchange, the recommended way is to use statement.

? we are using statements.
The statements pick-up the line waiting in account 403x (in our French case for exchange bill vouchers).

As I mentioned above (and in One Payment for multiple Invoices), standard payments with compensation accounts need to allow compensation accounts to have party_required . Also, delegate_to needs to be used.

If this were the case, then perhaps grouping in the compensation account is possible.
But notice then that grouping is an manual extra step that should probably be dealt with directly in payment and payment group (perhaps a special case of manual?)