It takes two to sit around and transfer cash, and there is no way to stop it afaik.

Apart from:

Using Ioncross Server Operator to kick and ban people generating too large a quantities of cash when at a low level, stopping new character creation for a week or so perhaps as well (which means they cannot abuse it).

Sure, you may not have a few new members for a short while, but forcing them to go and do something may improve things - or just kick/ban them. Find their accounts stashed with cash from such activities - and remove the cash /ban them.

There are more ways than one to skin a cat you know.