How do I choose several optimization parameters, leave the others constant in the calculation of non-linear constraint optimization.vi?

[getdlts]

Hello?

I posted "Optimization and Calibration with Simulation - Calculate Parameter.vi" provided by NI. 

In that example, I'd like to fix spring constant, while leave step time freely.

I know that is weird in that example, however, in my case I have to do it in my purpose.

Please help me