Can a banker overrule HR?

Hey guys here's the situation,

I had a first round interview with HR for an ib analyst FT position, which I think went ok. The next day there was a social event for all applicants (some of whom had not yet had their first rounds) and during that I had a very lengthy conversation with a banker (equivalent to somewhere between associate and VP) from a particular industry group and I expressed my interest in that industry so he took my name down and said he'll speak with HR to try to get one of the people from his team to be one of my interviewers in the 2nd rounds (obviously assuming I'll get through or that I was already through, understandably bankers may not be very familiar with what HR is doing at any particular time). We parted with him saying "see you at the interview".

Come few days later I'm told by HR I did not make it through to the 2nd rounds and considered my application closed. The banker did not give me his number but I can probably 'acquire' it through some other connection within the bank. Is there any point in calling him up and seeing if he can do anything for me if his still interested? Or are bankers generally very reluctant to second guess HR's decision unless it's a really exceptional case (which I doubt I am). What should I tell him if I do decide to make the call? What's the best time to call? I know I probably have nothing to lose but don't want to make him feel awkward either.

Thanks