Presumably you could bypass the regulator on the campfire unit assuming it's not regulating to a vastly different pressure. Depending on how it's constructed, that may be simple or rather complicated and impractical.
It is certainly possible to install a high pressure fitting of some sort for this (or other high pressure appliances), and people have done it for various purposes. Properly done, I don't see where it would be any more dangerous than toting around a 20 pound tank with its high pressure fitting, and probably safer overall. Improperly done, I wouldn't want to be nearby if at all possible.