Switching between email accounts once in outbox

[B100]

Ok this might seem like a silly problem....which it is due to my email setup at work. In short, when i am not on my network at work I cannot send emails via our Groupwise server (IMAP setup on my iPad). In such a case I just change my account to my mobileme when replying. But, sometimes I reply to an email forgetting to change my account which means the email sits in my outbox and i cannot send it. On my iPhone 4 I can edit the account on the email in the outbox but on the iPad it does not seem that I can change on the send account once the email is in the outbox. Is this an OS issue or am I just daft?

Thanks for any help!!