sorry I don't use the Massoth Switch decoders so cannot comment from experience, but...
As has been mentioned, I don't think there's a decoder definition for the Massoth Switch decoder. However as the Massoth unit appears to be programmed using standard CV values you should be able to use the JMRI DecoderPro Service Mode programmer, manually select the NMRA "Raw CVs" decoder type, open a Comprehensive Programmer and then use the CV tab to enter values directly into the CVs. Try "read full sheet" first to load current settings, and don't forget you need some sort of load attached to the decoder to allow SPROG to read the responses. You'll have to read and follow the instructions in the Massoth manual as to what values to program to what CV - there's no "user-friendly" programming in this case!
Do you use Loco addresses or Accessory addresses to change points (according the manual the Massoth decoder can use either?) I'm only familiar with using Accessory addresses with my NCE switch decoders. Reason I ask is that I found that I needed to configure JMRI to use the SPROG "Command Station" connection (not the usual SPROG connection) to actually test operate my switch decoders after programming. Remember to change JMRI back to the normal SPROG connection afterward otherwise you'll be wondering why you cannot program locos with the Service Mode programmer any more!
