Limit a range of date in a prompt filter

Hi,

I'm trying to built a prompt filter which permit my users to prompt a range of date (ex starting date - ending date).

But I would like to limit the range to a maximum of 50 days (from the starting date to the ending date)

Is it possibile to do it (in WI or BO 6.5 Designer) and how?

Thank you in advance

Riccardo