I doubt it can be done spanner. We recently bought a small home roaster after my other half persisted with the bbq rotissorie (that he had modified), without a great deal of consistent success. If your brother in law grew the beans he has to soak them them mash them with a stick then hand pod the beans. (All of this I'm sure he knows) Then they have to be dried. Makes buying the green beans sound easy.
When using our roaster it has to be preheated then the beans are put in and the temp raised to about 220 degrees I think.The roaster tilts and different angles as it is going and there is a paddle that seems to evenly distribute the beans. Much as I love the TMX I this is a little out of its territory.