Axe,
The only way I can think of is through VBA; you could add a routine that
checks your conditions and alters the .BackColor property depending upon
its output.
Attach this procedure to the control_Change event and there you go.
However, if you have lots of controls that you wish to work with, it may be
better to write a routine that tests all conditions and modifies all of the
controls; then simply place a call to this routine on the Change event of
all controls.
Not very elegant, but to be honest conditional formatting is usually used
to represent traffic lights - either red, green or amber; therefore not
usually needing more than three conditions.
Hope that helps
John Webb