How to make an Expression Field dependent of the load case in a Static Linear Perturbation analysis?

Hello,

I am using a Static, linear perturbation step that analyzes hundreds of load cases defined in the Load Case manager.

It is great for unitary loads, because I can script the scale factors for each load case and for each load.

However, I have a more complex load defined with an Expression Field.

Let's say the function is equal to X + 1. Is there a way to make this Expression Field dependent of the load case. For example :

Load Case 1 : Expression Field = X + 1
Load Case 2 : Expression Field = X + 2
...
Load Case n : Expression Field = X + n

For now, I have to define an Expression Field for every Load Case, and call the right Expression Field in the load definition, and then create as many loads.
Basically, I would like to define a single Expression Field for the load, and make it vary depending on the Load Case.

Thank you in advance for any help.