Bruce, you have a few options.
Least expensive: You can manually query each CV and manually write the value into each pain (pun intended) of the JMRI Decoder Pro. This is done with no added hardware. Programming on the main query uses CV64 to query whatever CV of which you want to know the value. e.g. to query the value of CV 4 you simply use POM CV 64 = 4. The decoder will 'speak' the value of CV 4. You might want to turn off CV 62 ("Talk back") feature before doing the query. i.e. Cv 62 = 0
expensive: You can purchase a programming track booster e.g. Soundtraxx, DCC Specialties programming track booster * caveat - these do not work with all makes of sound decoders.
Most expensive: However, certainly more practical than the booster - you can purchase a NCE Powercab and NCE USB interface (to access your computer). The Powercab was designed after sound decoders came about, thus it has sufficient current to query all makes of sound decoders on the programming track. No need for additional programming track booster. The additional benefit is the Powercab works like a Procab when using the layout DCC system. If your system is radio equipped you can even purchase an optional radio to make the Powercab into a radio Procab when using the radio equipped DCC system (cannot be used in 'Radio' mode when used as the programming track Powercab).