install cobalt intermediate steering shaft problem

I'm replacing the intermediate shaft (and the rack, for that matter) on an '07 Cobalt. I'm having great difficulty getting the shaft boot
to seat into the opening in the firewall. The boot has a 'doughnut' that's supposed to pop through the opening, thereby locking the boot in place. I haven't been able to get that doughnut to pass.
The Chevy book just says "Seat the intermediate shaft seal using a pushing, squeezing and twisting motion until seal is fully seated," and to do this before attaching the shaft to either the rack or the steering wheel. I've tried it that way, as well as with either or both ends attached. No joy.
This guy [1] says something (right at the end) about "pushing [the boot] through from the other [engine?] side," after he'd attached both ends of the shaft. I assume he means 'pull', but I'm not sure how you would do anything from that side, given how restricted the space is. In any case, I got nowhere.
AFAICT from Google/YouTube, I'm the first person to have this particular problem, which makes me think I'm missing something. If there's a trick, I'd appreciate hearing it. Or even just, "Yeah, it's hard," or "It's a piece of cake." Thanks.
[1]
https://www.youtube.com/watch?v=6T2oXeNvdQI&t@4s

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