Yiimailer: How To Send Both Text And Html Versions Of The Email?

So, due to some attachment-related bugs in the version of PHPMailer that the EMailer extension uses, I’m in the process of switching a project over from Emailer to YiiMailer, which uses a newer version of PHPMailer. I’ve gotten it mostly up and running again, except that I can’t seem to get the AltBody to work. I have two prerendered email strings, one for the HTML body and one for the text body. Right now I’m setting them like this:

$mailer = new YiiMailer();

... (Other settings here) ...

$mailer->Body = $htmlBody;

$mailer->AltBody = $textBody;

$result = $mailer->Send();

This worked in EMailer, but in YiiMailer, it only sends out the HTML body, and the text body I get is just a garbled form of the HTML body. If I dump it out after setting it, I get the right data back, so I guess at some point after this it’s ignored/overwritten. Is there a way I can fix this without modifying PHPMailer/YiiMailer itself? Some param I can pass in?