Multi-Signed Transaction - How to choose who pays for a transaction?

[subasm]

Given a multi-signed transaction, how can I choose who pays for a transaction? Currently it always defaults to the Account field, but in the case of some form of proxy execution, one of the other signers might want to pay the transaction fee.

[at3n]

I don't think it's possible - the account making the transaction must pay the fee.

I couldn't find a direct reference to this online after a quick search, but from https://xrpl.org/transaction-cost.html#insufficient-xrp:

Quote

When a rippled server initially evaluates a transaction, it rejects the transaction with the error code terINSUF_FEE_B if the sending account does not have a high enough XRP balance to pay the XRP transaction cost.

The "sending account" is presumably the one listed in the Account field, so this wording implies that there is no intention for there to be a way to specify that a different account pays the fee.