How to override custom mouse cursor with Xcursor?

When I use rdesktop to connect to a Microsoft Windows server, the mouse cursor is set to a monochrome version of the Windows true-colour cursor. This ends up being a white arrow with no outline, so it's very difficult to see it over a white surface. I don't want to change the cursor on the Windows machine, but my understanding of how Xcursor works is following: When any cursor is set, it is looked up by filename (using a hash of the cursor image) so that if a match is found, that Xcursor is used instead of the original monochrome one. My idea is that if I can supply this file and put a clearer cursor image in it (like the default arrow) then it will solve my problem by using the default arrow most of the time. Plus it will still allow rdesktop to change the cursor to something else (like a resize arrow) if the remote machine needs to. * How can I find out what hash to use for the rdesktop cursor image I am getting? * How can I map that hash to the normal arrow cursor in the theme I am using?