You may have noticed that EL in Intuit Link is not really an EL.  It's merely a Y/N response and there's not even a place for the joint filer to agree to the T&C's.

In that regard, if you need your client to agree to any additional terms, you can just add a new item to the Question section of Intuit Link.  Your client can then respond with a Yes or No to that.  That's assuming you'll build the proper terms to refer to how the new or additional T&C's will alter or add to those in the original "EL".