allow multiple selections in 2nd box of cf_TwoSelectsRelated

Greetings. I'm very new to ColdFusion, so I apologize if this seems like a no-brainer.

I've successfully used cf_TwoSelectsRelated to add related selects to a form. I'm able to have a user select a school, and have the second select box retrieve only the teachers that are from that school. Now I'd like to allow multiple teachers to be selected from the second list (to register for a workshop) and have them all be inserted in my registration table as individual records.

I think I can figure out the second part of my task (insert them as individual records) based onDan Bracuk's answer to a query back in February. However, for the first part (allow multiple selections in the second select list) I'm not sure whether to:
a) try to edit the cf_TwoSelectsRelated custom tag (I think I would need to know some JavaScript for that? yipe!)
or
b) do something to my existing code to allow the second select to have multiple selections (but doesn't cf_select just require that you specify in the attributes "multiple="true"? which means I will probably need to edit the cf_TwoSelectsRelated custom tag (back to *yipe*!)

Can anyone point me in the right direction? I've attached cf_TwoSelectsRelated. Please let me know if you need me to supply my code.
Thanks very much in advance.
Marianne