Pick her up in what he didn't know. Bart wasn't thinking that far ahead. Maybe he could actually pick her up and run them to some place to eat. Wally was always saying that was the way to take a girl out on a date-- and Wally got lots of girls to go on date... though Bart had no idea what happened to most of them after said date ended.
"Hey um... do you like... like... uh... bread?" NO that wasn't what he'd wanted to say! Stupid mouth getting in the way! "No! um- Paris? Do you like... you know... Paris?"
He knew he probably shouldn't give away his secret identity and all-- but when he thought back to his mantra of What Would Batman Do, he figured that there wasn't much Batman wouldn't do for a pretty girl. C'mon now, Batman wasn't an idiot.