In EG 4.1 you can use Project Parameters to create a parameter as a placeholder for a variable name in a task. (Tools->Parameter Manager, then define a new parameter of type Variable).
Most SAS tasks will then accept that parameter as a value you can assign in the task's roles page.
However, if you are looking to check for a condition and execute one set of PROC code versus another depending on the value of the condition, that's not something that EG will facilitate via point and click. But you certainly can write your SAS program in EG and then convert it to a stored process. You can even use project parameters to parameterize your program in EG, so that you are prompted for the condition values as you run it. The project parameters are then translated into stored process parameters automatically.