He actually broke through the doors twice. During the syndie run, he had to kick and punch the door to break through it, and when he busted out, he spit out some pieces that accidentally got in his mouth!
Other entrances....
On MG 74, he was posed on the big "O", and the O suddenly moved stage left, taking Gene with it, and then it moved back. Gene appeared to be surprised, and Richard quipped "Do you know the time for the next "O"?
Sitting on a chair reading a newspaper
Lying flat on the floor, almost like he died (GSN, not thinking clearly, aired this episode on the actual day Gene died) CNR runs up to "revive" him
Gene's makeup man is making him up, Gene looks in a mirror like Narcissus, and kisses the makeup man on the cheek.
When the doors open, Gene peeks his head out, and mouths "Do I come out now?" and the panel encourages him out.
Gary Burghoff entered with Gene a couple times, and in a rare moment, Gary actually waves with his disfigured hand. Another time, on MG 78, as a gag of a previous entrance where Gene came out carrying the children of Gary Burghoff and Patti Deutsche, the next day, he comes out trying to carry Gary and Patti!
He wore Brett's eyeglasses, and walked out like Mr. Magoo. Brett was laughing hysterically.
In a variation of trying to jump through the O, once, he pretended he was drowning, then struggles to pull himself through the O.
Once, the doors opened and as Gene walks out, the doors close back up! They open again, and Gene is holding his nose as if he hit his nose as the doors closed.
Peter Marshall and Gene switched places, and Peter entered instead of Gene. Apparently, there was a running gag that Gene and Peter were often mistaken for each other (other than the overbite when they smile, I see no resemblance) and they wanted to see if they could fool the audience.
On MG 75, he walked out like a robot