If you have to use struts, don't use straight mortise and tenons.
You could use a 'suicide' tenon which is a tenon inserted into a mortise that is wider at the bottom and expanded with wedges driven into kerfs in it so that it can never come out again. This is a joint I am familiar with in furniture, but haven't come across it in framing. You have a flared mortise, as described, and a tenon with maybe 2 saw kerfs cut into it. When this joint is put together, you place a wedge in each kerf and then drive the strut home. The wedges expand the tenon inside the mortise, and it can't come back out. This joint resists tension, which is its function in furniture joinery.

Or a lap dovetail could be used to resist tension.

Or, like Tim says, you could just not use struts as they would interfere with interior space.

Another solution is that you could build a truss with a profile kind of like this, which is sort of like an upper cruck, or a German Liegender Stuhl, depending on whether you use straight or curved supports...



This is I imagine a great departure from Jack's design..

But a higher knee wall is possible, it just may require rethinking the roof structure.

note, this drawing is just a very quick sketch, there is nothing technical about it.

I don't imagine that strawbales would do anything for you in resisting thrust. I don't know much about them, but imagine that any structural properties would be along the lines of bearing vertical loads