Still, I think there's something kind of undignified about prefacing the paper with "Uh, well, I'm going to retract some things that I say here, so...well, anyway."
Not at all.
At the very first conference I ever attended (as a first-year doctoral student), I went to a session where two people (co-authors) from my school were delivering a paper. (One was a Very Famous Senior Scholar and the other was a second-year doctoral student.) At this conference, which is held by the premiere national organization in my field, there are no commentators or discussants, but presenters must submit their papers to the conference way in advance, and all the papers are published into proceedings, which are then given to all attendees at registration. As Very Famous Senior Scholar got up to speak, the student co-author began distributing a one-page (two-sided) addendum (something I've still never seen anyone else do). And the Senior Scholar's first words after greeting everyone were something like this:
"As you can see, <student co-author> is handing out an addendum to our paper, because we now think the original paper was wrong. We've done some further analysis, and what we've discovered is...."I asked both authors about this later, because I was so surprised that you could
do something like that. They pointed out that it would be stupid to present findings that they no longer thought were valid, when what people want to hear about is what
is valid. It was too late to change the paper, so this seemed to be the best way to present the results of their final analysis. After all, they said, the whole point of the conference was to share and get feedback on what you've learned, so you might as well present what you've actually learned, i.e., the most up-to-date understanding of your data.
The session, BTW, went very well. People actually seemed to appreciate the updated results, and there was a lively (in the good sense) Q&A session, including many questions from other Very Big Names.
If this approach is comfortable for you, beardman, can't you preface your paper with an acknowledgment of the problems and tell the audience that you will respond to those after reading the paper (as is)? (Be sure to credit--and thank--your commentator for helping you to identify these problems.)