It depends on what you mean by "support".

As you've noted only three basic time signatures are offered.  It's my understanding that, to work in 2/4 for example, you would choose 4/4 and change the grid to 1/8 (notes) to create 4/8 time.

With MMM being a budget software package, your options are going to be limited.  A true DAW, like Samplitude, would probably offer more options.