I can answer this, as I am (what I know so far) one of very few that has put a leather strap to the OR deployant.
It IS possible, but you need to first get a strap that is prepared for springbars in both ends as the strap needs springbar attachment both to the watch case and towards the clasp. That is not possible with a Breilting strap so you have to get it custom made. Secondly, you need to measure the straplength carefully before ordering. Of course you can cut it like the rubber strap, but then you also need to have multiple springbar preparations. If you look close at the rubber strap you see that's the case and that's what makes it possible to cut it.
Edit:
See here what I mean.
This is the rubber strap end that goes into the deployant clasp. You can see there are multiple places to put the springbar (after cutting):
And this is how it may look with leather:
