Some good points, and I don’t mean to argue, but I continued playing as an exercise for myself and anyone else that may run into this.
It actually is possible to have this work with secure forms if we treat this as a standalone form and use the advice on this wiki page.
So, a stand alone comment form with a custom landing page might look something like:
<form id='comment_form' method="post" action="http://www.example.com" >
<div class='hiddenFields'>
<input type="hidden" name="ACT" value="1" />
<input type="hidden" name="RET" value="http://www.example.com/landing-page/" />
<input type="hidden" name="URI" value="/test/" />
<input type="hidden" name="PRV" value="weblog/preview" />
<input type="hidden" name="XID" value="{XID_HASH}" />
<input type="hidden" name="entry_id" value="1263" />
<input type="hidden" name="site_id" value="1" />
</div>
Name: <input type="text" name="name" value="" size="50" /></p>
Email: <input type="text" name="email" value="" size="50" /></p>
Location: <input type="text" name="location" value="" size="50" /></p>
URL: <input type="text" name="url" value="http://" size="50" /></p>
<textarea name="comment" cols="70" rows="10"></textarea>
<input type="checkbox" name="save_info" value="yes" /> Remember my personal information
<input type="checkbox" name="notify_me" value="yes" /> Notify me of follow-up comments?
<input type="submit" name="submit" value="Submit" />
<input type="submit" name="preview" value="Preview" />
</form>
Change out the RET value and the XID value from the generated code and things should work as expected. Also, that wiki page has some tips on using the captcha.
Again, as Pascal pointed out, this is not ideal because it is almost sure to break in certain situations, and you always run into problems with hacks like this when it comes time to upgrade your system.
Thanks again for the insights, Pascal.