Since GMs control the availability of coin in individual campaigns, a hard and fast rule other than NOPE would be pretty difficult. Regardles, I'd suggest it be very, very rare that the opportunity even comes up. Possibly the GM could create some windows - moments where a major presence is in dire need and a big infusion of cash would solve the problem, but I personally would never make it any
sort of scalable, at-player-discretion opportunity for dumpping loose change. Little coin does not buy big coin; that's the point
of having two systems.
Basically make it an adventure goal where the challenge is turn over a heap of money rather than kill a critter or manage a skill check.
The movie Blues Brothers comes to mind...