If you want a migration path to a site, you'll need to provide ample evidence that you actually have a sufficient demand for it. You need a significant number of questions that you either have already migrated to Stack Overflow, or are valid migrations to Stack Overflow that have yet to be addressed. Provide links to all of these incidents. Usually, this is in proportion to your traffic - it has to represent a path that is consistently in use, not just something that makes sense. Keep in mind as well, as you are a Beta site, it isn't traditional to allow migration paths to or fro with graduated to ungraduated sites.
Consider Gaming and Game Development - it makes sense to have that migration path, eh? Most of our migration-worthy content goes to Game Dev. But Gaming has only migrated 9 posts to Game Development over the course of a year. That's not really enough to warrant a migration path to be constructed. You want to be shooting for a high number of examples to provide.
When you've gathered enough evidence of the need for a migration path, then we can look into setting up a migration path. I mean, given you're Programming Puzzles, which basically split off from Stack Overflow, I can easily picture the migration path being valid. However...
In the last 90 days, there have only been 4 migrations out of here, only 3 of which went to Stack Overflow. There are only 3 other migrations, totaling 6 migrations to Stack Overflow over the entire history of the site. I think you'll have to wait until much better evidence accumulates.