In task manager is there any way to set user variables

Summary:

Anyway to let user set user variable before launching a business rule via task manager / task or to have the business rule only run when explicitly launched by the user, and to prompt the user with rtp in the normal way - that was all there in task lists.

Content (please ensure you mask any confidential information):

Using task manager I can run business rules. They auto run, not so good. I can use substitution variables - okay. I cannot use run time prompts - ?!? As a workaround for not being able to launch the business rule passing rtps as I could with the old task list I am looking to allow the user to set a user variable and to catch that in the business rule.