How to cast to type Process Model?

How can I cast a value to datatype "Process model"?

I want to dynamically start a process model using

a!startProcess(processModel, processParameters, onSuccess, onError). I know that I can create a constant of type process model and pass it to parameter processModel.

However I would like to make it more dynamic, so that I need not create a constant everytime I want to call a new process model in future. Instead, planning to store the process model ID number in database and type cast it to "process model" and pass it as a parameter to a!startProcess().

I learnt that casting to type "Process Model"is not available in https://docs.appian.com/suite/help/19.3/Casting.html#general-casting, and anything that is not the list cannot be cast or will throw an error. Could anyone please let me know if there is any way we can achieve this. 

I also learnt that we can make the design dynamic by using decision tables to map Process models and then use Start Process Smart Service. However, if I want to call a new process in future, I will still need to make changes to the decision table and deploy a new version. So, I am checking for getting the database approach I mentioned and using a!startProcess().

Thanks in advance!