I know what you mean but it's up to the touchpad manufacturer to make the driver work when you are running as another user. Sadly nothing can be done.The major reason why I don't use/test ReHIPS now is it's not fully compatible with my touchpad driver with regards to sandboxing some application (i.e. Touchpad gestures wouldn't work). Because of this "incompatibility" my usage of ReHIPS would be limited to some applications and the use of the HIPS.
Assuming it can work when you are on the same desktop the issue will be solved though.