Here is an important question: do you plan on mashing the dark grains with everything else?
Dark grains, like crystal, don't really need to be mashed. So you have a number of options for treating them. Depending on the recipe, you could cold steep them separately from everything else (overnight at room temperature should do the trick), then pour that liquid into the boil with, say, 10 minutes to go. That will yield a very smooth, less harsh taste, though you might not want that with an RIS.
Even if you don't do that, though, you could hold back the dark grains for a separate steep (say, in a stockpot). This would allow you to use the "base" malts (or whatever you put in the mash) to make first runnings for an RIS, and second runnings for just about anything. I don't know your recipe, but you can imagine examples--an 80% pale, 20% Munich base could be used (when dark grains are added) for a stout, and then the second runnings could be used for an IPA (with different specialty grains).
If you do mash everything at once, you're a lot more constrained. Bear in mind that the second runnings will have less desirable flavor--they may be somewhat more grainy, less malty, perhaps harsher tasting. That might counsel against making a straightforward malty beer (e.g. brown, porter) and in favor of making something that relies on other, more complex flavors, like hops or fruit, which would mask the roast. When I recently made an RIS, I used the second runnings to make a cherry stout (still aging), on this theory.