displaying "why" when conditions reject workflow steps

I added a custom condition for making a field required at a certain step in the workflow. (the condition is that a selected field must be entered prior to executing that transition.

Unfortunately, now when the user hits the prior step and the field is blank, they simply don't see the option of executing that transition. There's no way for them to tell why.

What I'd like to see is when configuring a condition, to have the ability to type a value into a "why" field; if that field is blank (which it would be by default) everything would work as today and the user wouldn't see the transition link. If the field was populated, the transition link would appear but the field would either be disabled with hovertext containing the "why" messages collected from the various conditions that said no, or the link would be enabled but would cause a popup window with the "why" messages