Check this link for your problem.
to see suggestions.
And my opinion is If you are using Jquery then create listbox in jquery .
then using jquery post that data to server side whenever you like .
I hope you know that listbox is nothing but select tag .
this type of situations are dealing in jquery is easy than creating controls in asp.net
I hope you understand what i said.
Sure you can find solution in above link.
All the Best.