How to convert MT -> WP preserving post IDs?

I’m trying to move from MT to WP, but I have a major stumbling block. My URLs look like this:

https://www.example.com/posts/001234.shtml

The 1234 is the postid. To preserve my URLs I need to be able to move the post IDs from MT to WP, then make WP pad the post ID out to six digits, as above.

I’d like to avoid having to use redirects. I have over 4000 posts, lots of internal links, and lots of inbound links that boost my Google PageRank and bring search engine traffic.

Any ideas? I’d consider paying someone to help me with this, because it ain’t fun.