I have very VERY good techniques for doing this using Scrapebox... techniques that will see the majority of auto comments being on subject and also being approved by the admin. You just need to think outside the box.

I'm not going to give all the details in here though purely because it could open up a spammers paradise, especially if not followed 100%.

So as suggested above... extract all the on topic, high PR posts and manually write a good comment.

It is actually quite easy to write a sticky comment with scrapebox but you have to be really careful with it. I just checked my backlinks for a brand new site that I did a scrapebox run on and yahoo has 441 backlinks indexed for this site already! Not good... Luckily it has not had a negative effect on serps... Yet. The site actually moved up a page. I didn't think the admins of these site would approve the comments so quickly. Here is a quick tip though that will allow you to get a few extra links without stressing yourself out about writing a "sticky" comment. Use the blogengine feature. These blogs approve comments faster and at a higher ratio. The only thing is it is ultra slow so be sure to do it before you go to sleep or something.