Here's and easy way. On the full boil, bitter with Nugget. Late hop with the Cascade. After fermentation is complete, split into two 3 gallon carboys. Dry hop one with Nugget, the other with Cascade. Two ounce minimum for each. A lot of aroma and perceived flavor come from dry hopping. This should give you a good idea of what each hop has to offer. You could blend in the glass to get an idea of what the combination will produce. Not the perfect solution, but easier than splitting the boil.