Collision between Transaction::Simple and ActiveRecord

I want to use PDF::Writer from Rails. Which works, basically, except for the ugly error messages when PDF::Writer loads Transaction:.Simple, and it tries to define its own constants -- which have already been defined once by the copy of Transaction::Simple that's wodged into a corner of ActiveRecord.

Now, I can play silly buggers in my cron scripts and such to filter out those error messages, but that's quite a lot of work to get around an exceptionally bad design decision in ActiveRecord. So I'd like to know if there are any reasonable ways to either get ActiveRecord to use the real gem-installed Transaction::Simple, or to get PDF::Writer to use the one included in ActiveRecord?

(Problem exists with Rails 1.1.6, on at least RHEL4, FreeBSD 6.3 and MacOS X 10.4.8).