Navigate: PeopleTools > Process Scheduler > Processes > Select your process
Process Definition Options tab, Process Security area.
Hit the + sign in the Process Group area and add a new Process Group, this is a no edit table prompt, so you can add any value
Save Process Definition.
Now navigate to PeopleTools > Security > Permission Lists > Tab Process
Add newly created process group to a (new) permission list and assign permission list to (new) role and assign role to user.
Now the user can run this process.
Do this repeatedly for all your processes.
Be aware to keep the number of custom Process Groups to a minimum to keep a clear overview.