I don't think that there is anyway to have and SSRS report export to Excel and have the spreadsheet have drop-down's. I'm pretty sure you'll need to find another solution for this.
Jack Corbett
Consultant - Straight Path Solutions
Check out these links on how to get faster and more accurate answers:
Forum Etiquette: How to post data/code on a forum to get the best help
Need an Answer? Actually, No ... You Need a Question