There really is no way to help they will instantly attack you. sorry...No you can't pay a fine, that would make everything too easy. Let me think...... Try putting on some NCR armor on, that MIGHT work. (have tried that, he still attacks me. NCR armor got into McCarran of ALL places, but Andy can literally "see thru" your diguise easily...) This is BS cause now I can't complete his quest right? Go to the Vegas strip, eventually (possibly after meeting with House at the Lucky 38) a NCR trooper will approach you and deliver a request to visit the embassy. Once there, talk to Dennis Crocker and he will assign you the quest Things that go boom. Once that quest is completed, your NCR infamy will be reset to 0 depending on how it's finished
Other than that bein Vilified is a death nell man. You can't get out of it all rangers and centurions can see through disguises.
If you haven't been to the strip yet there's a rep reset that'll take place there. Otherwise try to help out at Sloan and the Crimson Caravan, that'll help your NCR rep. Otherwise you're probably just out of luck, it wouldn't be the only quest that you can't complete by taking sides.
You can get a faction armor and wear it. That should stop the problem.
sneak into helios one and finish the quest with sending the energy to vegas and mccaran is also possible