Well, in effect you're saying that when it's -40 in FAI I can push the engine to 120ish% N1 (red line 105%) and still not be at the engine limit... I don't think so.
I would like to see you try! These things have EECs to ensure you don't.
But maybe what I am saying is that if you select TOGA thrust and your EGT is below 750 deg C then the time limit would not apply.
I have yet to find where is says the EPR time limit (or any time limit on any EPR setting). Maybe someone can point me in the right direction?
Here is the JAR type certificate for the B757-200:
http://www.caa.co.uk/docs/1419/srg_acp_fa28-05.pdf
Maybe you could point to where the EPR time limits are established? The rotational limits are there but not the EPR (thrust) limits. Surprisingly the EGT limits specified are above those in the Boeing FCOM.