Colm Meany didn't want to be a regular, either. He liked his limited roll on TNG, which allowed him the freedom to disappear whenever he needed to do a feature. Berman had to promise to still allow him considerable freedom in leaving DS9 for certain periods to do features before he would agree to be a regular.
He fondly described his role on TNG as an "irregular regular."
Up until the third season, O'Brien did almost nothing but transport away teams. I remember being surprised at the third season episode where O'Brien has his first onscreen phaser fight and gets shot. Until he came stumbling over to Riker, I thought he'd been killled.
