Cast Member ticket discount upgrade?

[magentarhps93]

Hi there! I'm traveling to WDW in June with my family and best friend and we will be visiting my friend who is a CM. She was nice enough to buy my friend her tickets with her CM discount, but CMs are only able to purchase up to 5 day PH tickets, and we will be going to the park 7 days. I was wondering if anyone knew if it was possible to upgrade the tickets bought with the CM discount. I know we wouldn't get the discount on the extra 2 days but it looks like the only difference between 5 and 7 day tickets on the website is $20. Is this all we would have to pay? Does anyone have experience with this, or should I just call Disney?

Thanks!