How to move Wordpress comments only from one domain to another?

We have a bit of situation here. We have a website (let's say it is www.oldsite.com) where we had more than 2000 posts. There arose a need whereby we had to move some 60-70 posts from this oldsite.com to another domain of ours (www.newsite.com)

So, here is what we did:

1. Move those 60-70 posts manually from oldsite.com to newsite.com Did a 301 redirect of each of those 60-70 posts from oldsite.com to newsite.com. Google has now started to rank the posts from the newsite.com for this. That's all good till now.
2. Now, here comes the situation. We also want to move the comments from some of those posts from oldsite.com (some 10-12 posts out of those 60-70) to the respective posts of newsite.com.

How do we do that? Do note that we are pretty comfortable with databases and to some extent PHP. Please help.

Thanks.

Note: We did ask this question on a couple of other forums as well and on WP @ SO but were not able to get any help

Shalin