I've got a potential solution to the issue you're describing here.
I created a component in my library called 'BSource' with a symbol and spectre view only (just copy a vsource symbol).
Then, I edited the CDF to have the following:
Parse as CEL: Yes
Parse as Number: No
Simulation Information: spectre
termOrder: PLUS MINUS
With this, I was able to instantiate a BSource subcircuit with the following parameter:
I then could start up ADE, have it pull the parameters Fstart and Fgain from the BSource instance and simulate a transient chip simulation.