I promise I'm not trying to sound like an arse, but it's probably going to come across like it.
What's the problem with gatekeeping parkrun by putting a suggested time limit on a course? Sure, the organisation is trying encourage physical activity. But it's foremost aim is to encourage
running in some format (whether that's running, jogging, walk/run, buggy running). Either keep that or change the name and make the whole event last the entirety of a Saturday morning so that anyone who wants to can come along.
I think
@RunRunRun is spot on, but sadly I suspect there wouldn't be much support for that, from PB chasers or PR HQ themselves, given that they don't agree with permanent course marking signs in parks. I've never volunteered for a few reasons but the largest one is that I simply don't want to be standing in the cold for 2 hours on a Saturday morning. (I don't make it to PR that often, tbf).
When I was pregnant I deliberately didn't start with the rest of the pack and made it clear to the tailwalker that I wasn't taking part in the event officially as I knew I wouldn't finish under an hour. I just walked in the public area following the same route and giving way to faster moving traffic.