I got the Mallets for that purpose on my utility bike. They seem like they would work for a few miles as platforms, but they rub a lot of sole on my casual clipless shoes. The cleats come with shims, but they make the cleat scrape the ground. I took off the grip plates and it works better - hopefully that doesn't make them too slick as platforms.

It's actually a 6mm wrench, and you would need a cheater bar to get the same leverage on that as with a pedal wrench, and you have limited leverage options since the wrench hits the chainstays. I'm not saying it's ever impossible, but it can definitely be more difficult than it would be with wrench flats.