FEAT: Applying higher level analysis based on EVs, not copes

I’d like to do GLM task analysis, and I have long runs, and many types of stimuli that can later have a number of divisions according to a number of criteria.

Now, I’d like to run the GLM on those EVs (say, 12), and once the hard work is done, to create the contrasts on the higher level analysis, so I don’t need to run the whole thing for scratch every time I want to try a new contrast.
Is this possible? If so, how do I do it?

Thanks a lot!