I've done the same, combining juice with a large quantity of skins of a different varietal, although, in my case, the juice was a kit. You're right, it does make a very thick and sloppy concoction, but follow your normal protocol, punching down as best you can, checking SG of the juice (which is hard to pull out for a test, best done immediately after a punchdown), press around 1.000 as normal. In my batches, wasn't really able to draw off any significant amount of wine prior to pressing, so just scooped slop into the press and allowed the wine to flow out on its own through strainers. IIRC, a little stirring of the must in the press helps to release the wine from the press before actually applying any pressure to it. If you don't get most of the wine out before pressing, you might get some slop squishing out around the press plate. In the end, the product was just fine, and the wine was way better than just a simple kit, and didn't have any of the normally discernible kit characteristics. In the end, the yield was just fine, ended up with a full 6 gallon carboy after racking off of the gross lees. You'll do fine with this process, but it's a little more time consuming.............