I know of numerous traders who started like you describe.
Works particularly well on the West Coast for those with flexible schedules. They trade the morning session 6:30-8:30, and then go to work. Some also take a long lunch 11:00-1:00 to do the closing session and just work a little bit later into the evening on their day job.
Some work a job as a waiter in the evenings. Some deliver pizzas in the evening (these work on both coasts).
Just be careful about bartending... work till 2am, then have to trade at 6:30am? Will you have time enough to prepare? Will you get enough sleep to trade sharp?
I know of one guy who was an apprentice chef. He was working his way up the ranks and loved what he did. On the east coast, he traded just the morning session, made $300-$400 a day and then went to work. He only traded for extra income as being a gourmet chef was his true love.
Lots of ways to do it if you REALLY want to.