I may of misunderstood your question the first time. If you have the form open and the email address is in a field. This may work: Put Me.YourFiledName in the To part of the SendObject argument.
Just use your field that holds the email address in place of the YourFieldName.
In code you would do it like this:
DoCmd.SendObject acReport, "ReportName", , Me.EmailAddress, , , _
"OptionalSubject", "OptionalMessage", True