Ok there are two options for getting around this.

1) Instead of using the reply button, you can perform a "resend" on the sent item. Open the email message from your Sent Items and then click the Other Actions button and choose Resend this message. This option will have the recipient in the To field and will include the original body text also. You could delete body text if you wanted or just send a complete copy of the email.

2) You can Forward the email. I generally use this option as I can include a message like "Did you get my email below which was sent last week??". When you forward you will need to enter the recipients name into to the To field and it will give you a blank area in the body to type your next piece of correspondance.

Hope this helps.