Choosing an email account to apply from with MSE Outlook Web Access

Hi,
I work for small company which are using MS SBS 2003. Some of my colleague use two email addresses generated from the same server (call them “a” and “b”. So at certain times they reply either from the “a” or the “b” address. This is ok for normal MS Office Outlook, as they can easily select which account to reply from. However, when using MSE Outlook Web Access they can only respond from “a” and do not have the option of responding from “b”. Is there an option to reply from two different email addresses in MSE Outlook Web Access?

Regards
A