Adding commentary tracks from DVD to Blu-Ray file

[magnu]

Hi there

I have a show on DVD that has now been released on Blu-Ray. However the episodes on the Blu-ray run for an extra 70 seconds (there are no missing scenes). One of the reasons I am assuming is there's a different framerate between the two versions?
I was planning to copy the episodes I have where the DVD episodes have commentaries, to my HDD, so that I have a complete version of the titles.

Can anyone recommend software I could use to try this out with? Something Windows based preferably?