The diminished major 7th chord is the diminished triad with an added major 7th.

It was/is widely used in fusion and ECM type music as far back as the 1970's often rendered as Maj/b2. That was the era when everyone was using the modern triad system, where there was usually the triad over a non-chord member bass note suggesting the use of two keys simultaneously.

The best way to do it in BIAB is have as a first inversion 7#9 chord (Ab7#9/C). The implicit added #5 doesn't spoil the sound as it comes from the diminished W/H scale anyway.
In most cases B/C doesn't work well with midi styles because many of them have Major tonic chord riff figures that ruin the effect.

Sometimes the first inversion of B major, Ebm#5 can be used over C but even here you run into the same problem with minor riff patterns that use the 5th instead of the #5.

BIAB chord masks in the stylemaker have always failed to distinguish altered and suspended chords from plain unaltered ones giving you totally unwanted effects with riff patterns at times. Unfortunately they turn up a lot in modern jazz styles. My approach is to alter the pattern notation to get rid of 4ths 6ths and 9ths and/or turn pattern embellishments to 0.