I'm not quite sure what exactly you're trying to do. There's no reason you cannot use a case structure with a for loop, unless I'm really misunderstanding what it is you're trying to do.
It's possible you may find this example helpful: https://decibel.ni.com/content/docs/DOC-14687
They generate their ramp in a different way, but the idea is still the same: generate the waveform that you want to output and then send it to a device as many times as you want it repeated by using a for loop.
