"No, but thank you for considering me."

[Reuth]

I believe this is a variation of "I'm afraid that won't be possible." My co-worker said she uses it when someone tries to volunteer her for something, or presumes she will do something for them. Thought I would share.

[Mental Magpie]

I like it!  Especially if she wants to be considered for something else in the future, she has shown that she is grateful for the consideration of her talents.  I think it has better uses in the situations you described than in situations when someone just isn't getting the point.  In the latter cases, I'll still use "I'm afraid that won't be possible."

[BeagleMommy]

Love it!

[NotTheNarcissist]

I like it! Hopefully I can remember it ...I tend to go brain dead at moments when I would need a phrase like that.