non deductible contributions

[Gary]

Say A db deduction limit is 100k and the employer contributes 120k.

That is an excess of 20k.

Pre PPA if a plan contribution did not exceed the full funding limit there was no 10% excise tax.

It appears now that 4972©(7) essentially allows an employer to elect to not take into account contributions in excess of such full funding limit and thus as I understand it "not be subject to 10%" excise tax.

Is my understanding accurate?

And if so, does the employer/plan sponsor simply sign off on an election prior to deadline for filing tax return?

And finally, while the 2010 tax return is not due until 9/15/2011, what can sponsor do for an excess 2009 contribution where tax return was already due and filed?

thank you.