Two options on a form that map to the same field

Possibly if you use the SOAP API/jquery

Why would you have two fields map to the same field?

Can you tell me your use case?

If your use case is just simply to know whether a lead is interested in either demo or info, you can create a smart list to find them without creating another field.

If you do want another field, you need to figure out what you want to do in each scenario

Demo - True, Info True => Contact Me = True
Demo - False, Info True => Contact Me = True?
Demo - True, Info False => Contact Me = True?
Demo - False, Info False => Contact Me = False

Next create a triggered campaign to update the contact me field when lead sets new choices ( based on logic above)

Smart List - Data Value Changes for either the Demo Field or Info Field
Flow -

(1) If Demo is true => Contact Me = true
(2) If Info is true => Contact Me  = true
(3) Default => Do Nothing.

(One time fixup) To set the Contact Me value based on your existing data value from info and demo field, create a batch campaign to do a one time job.

Hi Calvin, 

The different choices you mapped out looks right. We have turned to all forms on our site to map to contact me. On our advertising landing pages we still have the option of demo request and information request. 

Hi Alyssa,

Cool thanks for the info.  If you run into any difficulties setting this up, let me know.