Interesting but I'm pretty sure it's factually not possible. From what I understand Brian only heard he was going to be on the show after Black Frank was cut. And if this season had one constant it's that next to nothing was said to a contestant in the basement that wasn't immediately reiterated upstairs.
One of Brian's big refrains early on was "I don't even understand what I'm doing here": he was made to understand he was the sole plant and also only chosen to come on at the final hour, so in his mind Frank, the guy who is friends with Jezza, was somehow the sole trusted plant (extremely unlikely) or else there was no plant at all until the final hour before the show (which is a terrifying prospect for him). So no wonder he was panicking, the first explanation would be that he was brought in to get made fun of and instantly eliminated.
The original plan was probably to introduce him as a freeloader later in the show, and he'd become the cult leader. Black Frank was cut, so they asked him to fill in, and told him he was the plant. Nothing was spoken in the basement so the plotline stuff was less obvious, it was all discussed prior to the show's start. Brian's understanding then, was that there wasn't a plant prior to him filling in last minute. When the first plotline is that there's an "infiltrator," he thought he'd been setup, like you said, to be made fun of and instantly eliminated. Then the "everyone is a plant" plotline got revealed, he realized he wasn't any more of a plant than anyone else, and showed more relief than anyone else. Then he didn't understand what he was supposed to do: If he was a freeloader, and being paid, he probably thought he wasn't allowed to win, and the cult plotline was clearly not going in the way they'd previously discussed with him. It's probably why he was so proud of finding ways to get the audience to hate him, too: his goal wasn't to win, it was to contribute to the "story," and part of that was probably getting the audience to hate the evil cult leader while also winning over the fish.
It's like they hired an actor based on a role in a script, and then wrote out his part without telling him. He's still on the set trying to act, but the plot wasn't happening around him and it just confused him. Then Sam specifically said they decided not to use the cult plotline because it was too dark, so they wrote him out of the show via elimination because he'd successfully turned the audience against him and no longer served a purpose, hence him referring to production as "pussies."
The romance thing was probably part of the cult leader plot, too, now that I think about it: Trish may have also been a plant, which is why they were so straight forward about rigging it against her. It's probably also why they kept her around: they were friends with her and had hired her to be the cult leader's concubine. Probably why Brian ended up back at the end, too, the "psycho killer" bit might have been recycled from the cult leader plot.