[Byzantine]

Possibly. My original idea was that you had a list of powers for each level that you always had access to, aka the whitelist. Then, if you want something off the 'ban-list', you have to take a feat. This feat will give you a single power (subject to DMs approval) from the ban-list, up to one level lower than what you can manifest. There then would be an epic version that allowed you to use level 9 ban-list powers. Here's examples of my thought process.

Spoiler

Forbidden Knowledge [General, Psionic]
Months of meditation and self-discovery has uncovered a dire power within you.
Benefit: You may learn one ban-list power of any level up to one level lower than the highest-level power you can manifest. For example, a 7th-level psion gains either a 1st, 2nd, or 3rd-level ban-list power
Special: You can gain this feat multiple times. It's effects stack.

Epic Forbidden Knowledge [General, Psionic, Epic]
Years of focusing your power has created a powerful new ability within you.
Requirements: Manifester level 21
Benefit: You may learn one ban-list power of any level up to the highest-level power you can cast.
Special: You can gain this feat multiple times. It's effects stack.

Honestly, I haven't posted it in Tallal quite yet since I'm still working on the crunchy bits, but I'll post something about it here in a moment, just for you.