Self Employed Owner of a S-Corp

I am a self employed owner of a S-Corp.  My husband is my employee and received a W2 from my corporation.  I would like to contribute to the self employed 401K that I open for him.  I did not know I have to report this on his W2 can I still contribute?  If so where can I enter this information?  Do I enter it via the S - Corporation Tax return or on our 1040 form?