It just struck me that maybe when you say "display," you are not referring to the parameter drop-down but to the final rendered report output. If that is the case, what you need is a way to reference the parameter label in an expression instead of the parameter value, and there is an easy way to do it.

In a placeholder expression, this gets the underlying value (of course): Parameters!parameter_name.Value

And this gets the label displayed to the user: Parameters!parameter_name.Label

Hope this helps!

Geoff