Automatic Growing Textbox

I am showing a Multi Value parameter on a Report, in a textbox that has CanGrow = True.

This is fine when there are only a few value in the parameter, but when many values have been selected, the fact that the textbox grows automatically to accommodate the contents means that this textbox can become quite large.

I am using the value of:
Join(Parameters!ParameterName.Label,", ")

Is there any way to either limit the number of values of a parameter when displaying in this way, or of setting a maximum size for an automatically grow textbox?
Or anything else that would solve this issue?

Thank you very much in advance!