If you only have the one field, you can create a regular button that stores the password in a temporary variable, clears the field, emails it, then puts the password back into the field. Here's an example:
var mypassword = PasswordField.rawValue;//store the password field value in a variable
PasswordField.rawValue = "";//clear the field and the resultant xml
event.target.submitForm({cURL:"mailto:me@me.com",cSubmitAs:"XML"});//mail the form with attached xml
PasswordField.rawValue = mypassword;//bring the password back into the field
Another option, if there are many fields you don't want to be in the xml is to store all the xml in the variable then clear all the fields you want then re-import back into the form using xfa.saveXML() and xfa.loadXML().
Kyle