For me the problems were caused in the switch between default functionality in pecl_oauth 1.1.0 (this isn't a bug, but is correct behaviour according to the OAuth 1 spec, I just had code that expected the old functionality), so I wanted to put my version back to 1.0.0
pecl install -f oauth-1.0.0
It was easy once I stopped looking for an option called "downgrade" or something like that :) In fact you can use this trick to install all kinds of pecl versions, simply refer to the package as [package name]-[version]. By default pecl won't let you install packages that aren't marked "stable", but you can install beta packages by putting "beta" in place of [version].
Hopefully now I've written this I'll remember next time how to do it!