It may not be pretty but let's say you want to have three email addresses per person. #1 is default and #2 and #3 are whatever you call them. #1 uses the actual EmailAddress attribute, the others are text attributes. Then create #4 as a text attribute that is used internally.
You could make a process that has the user select which address to use, in this example, #3), then:
#4 = EmailAddress
EmailAddress = #3 (use the selected value)
Do your mail thing...
EmailAddress=#4 (replace the default email address)
It's a bit more complicated than this, but it's an idea if this is a must-have capability.