Never done it, but I've thought through it before. I would likely snag a few 600mL or 1000mL glass beakers off Amazon and put the beers into those for blending. I would start with 1/3, 1/3, and 1/3. Then maybe shoot for 1/2, 1/4, and 1/4 after you've found your base beers. Or even 3/5, 1/5, and 1/5. Honestly, taste over fractions is the way to go, but it's a place to start. If you blend from beakers, then if towards the end you wanted a hint more of beer #2, for example, you could pour some and see how much you took away from your beaker. Allows for more fine tuning. Again, never done it, but this is how I would.