Thats really not possible as the variable you are trying to do split on is not loaded at design time.
There is no such thing as an offline immediate panel.
You have to use documentation or run your code.
Its not a big deal to make an empty workflow with a breakpoint to test something like a split.
If you want more complex stuff related to your actual code / variables the code has to be running.
Think of the request like you are asking to taste the food in a restaurant by using the pictures in a menu. You have to cook the food to taste it.