solidworks driveworks express
I would think the simplest way would be to use configurations.
If you don't want to set each Configuration separately then it is simple to create a Design Table
You can't use Variable Patterns as a Feature of the Part if it's a Body. You can't use Linear Pattern in the Assembly because they cannot be made Variable
The only other way would be to pattern the body (in the Part) and then use the Direct Edit Move Face feature.
Set up the part using configuration publisher and you can create the required length/configuration on the fly or choose from already existing lengths/configurations.
Thanks for this tip, this is what I was looking for.