ieee membership discount on overlength manuscripts
I believe there is confusion about what the charges mean. Generally, IEEE has two types of page charges:

Voluntary Page Charges
Overlength Page Charges

In 2020, for IEEE Transactions on Information Forensics and Security, the voluntary page charge rate is $110, while the overlength page charge is $220 — which correspond to the numbers in your question.
However, the meaning of these charges is very different.
Voluntary charges – are actually voluntary. They are not obligatory, usually paid by the institution, and help IEEE to offset some of the expenses incurred in publication.
Overlength charges – are different. They have to be paid for all submissions exceeding X number of pages (X=6 and X=10 for short and regular papers in IEEE Transactions on Information Forensics and Security, respectively). This small note from 2004 might explain things a bit more elaborate; I simply was not able to find the relevant page on the IEEE site directly.
I have never heard of a discount on overlength charges. Often, these charges are paid by the advisor from a grant. I once paid the charges myself as a student when I was in transition between affiliations.
With all that information, it is highly unlikely that you can get the charge lower than $220 pay page over the limit. However, in some circumstances (the reasons have to be very serious), I believe IEEE can waive the charge altogether.

Disclaimer: I serve as a Vice-Chair of Membership and Benefits Committee for IEEE Antennas and Propagation Society; however, this answer is not within my direct area of expertise — thus, posted solely as my opinion as an individual familiar with IEEE practices.