I wish I could state that you can find a way around it, however in my experience you probably will not, simply because of your batch size. Assuming your french roast is pretty dark, somewhere within the 450-460F range, your going to be dealing with a lot of stored heat potential.
Your roasting around a 60kilo mass of agricultural material that stores a lot of potential heat energy through the roast, as you near 2nd crack that mass is going to want to go very exothermic, even if you cut flame entirely I still think they would ramp up in your drum to the point of "blowouts".
With that said, a smaller mass in a smaller roaster would be much more controllable within those temperature ranges because there is less mass to go "exothermic", therefore the beans could approach a "french roast" much more gently and with fewer blowouts.
I think you will have trouble trying to be as gentle as you can with 60kilos at such a high temp. Just save that practice for your coffee's other than those from daniel petersons estate lol.
Just my two cents,
Also, I myself do not practice "french roasting", to me its a roasting practice that will never hallmark the true flavor characteristics of a coffee, at that roast level you are "carbonizing" the beans and inserting false body and destroying the delicate chains and acids formed by a correct profile, taking it darker will destroy that work.
But hey, it does sell, ..... so I understand its place, this is after all a business.