Split squad games are negotiated each year as part of coordinating spring training schedules. Of course, to have a SS game, two teams must agree on a need on a certain day months in advance – and one of them will have to travel. It is not known that far ahead of time which days will be best to have more guys throw and how many innings will be needed. For hitters, it is easier.
It is far superior to remain flexible and schedule your own B games (or sim games) as needed on the back fields in the mornings. The team controls everything in that format.