Further on that, Snowden has still not faced trial or been formally charged with any crimes -- unlike General James Cartwright of Stuxnet infamy. "I can't pardon somebody who hasn't gone before a court and presented themselves," Obama said in November. Having a trial isn't a necessity for a pardon, mind you, but based on the President's comments at the time it doesn't sound like he was interested in broaching the situation that way.
"At the point at which Mr. Snowden wants to present himself before the legal authorities and make his arguments or have his lawyers make his arguments," he said, "then I think those issues will come into play."
As of publication time, the ACLU-led petition to grant Snowden full immunity was still roughly 500 signatures short of the 60,000 target -- up from 57,000 signatures in September.
It's worth noting that Snowden himself implored President Obama that if he only granted one act of clemency upon exiting 1600 Pennsylvania Ave to free Chelsea Manning. The president commuted Manning's sentence today and she will go free May 17th this year instead of 2045.