Start Marinade. Place all ingredients into a blender and run on low speed for a minute to chop roughly. Leave everything in the blender for now - you will be processing further in a little while; this allows the seeds to start softening so the mixture will ultimately be smoother.
*Note: Traditional puerco pebil uses sour orange juice, which is not widely available in the US. The lime and orange juices combine to form an approximation - if you can find sour orange juice, by all means use it. You should be able to get the juice you need from 3-4 limes (buy a few extra for serving) and 1 orange.
Prepare the pork. Cut pork into 2 inch cubes, trimming only the really large pieces of fat - you need some fat in this recipe! Place cubes on a tray and freeze for about 30 minutes.
Finish marinade. Resume blending the marinade - this will take several minutes. Stop and scrape down the blender cup frequently. Ultimately, you should end up with a fairly smooth, almost paste-like mixture that is brick red and appears to be homogeneous. Scoop out into a small bowl, and take out 4 TBs and set aside. Tear up the bread and stir it in (not into the 4 TBS portion).
Prepare the onions and corn. Slice the onion in half pole to pole, then further slice into 3/8" wide half-moons. Place in microwave safe bowl. Cut the kernels off the ears of corn and add to the bowl. Add 2 TBS water to the bowl and cover with cling film. Microwave on high for 2 minutes. Drain immediately and spread out onto paper towels to soak up any extra moisture.
When cool, replace onions and corn into the bowl. Add the queso fresco (crumbled into largish pieces) and reserved 4 TBS of marinade. Toss to coat evenly. Send to fridge for at least 30 minutes (you won't it again need until serving time).
Grind the pork. Run slightly frozen pork, bread and marinade from step 3 through the coarse blade of a meat grinder twice. Be sure that the spices and bread are evenly distributed. If you've opted for pre-ground pork, at this point just add the bread and spices and mix very thoroughly.
Divide pork mixture into 6 patties, about 3/4 of an inch thick. Patty well, this mixture is not as sticky as a typical beef burger mix. Pan fry or grill over med-high heat until cooked all the way through, about 3-4 minutes per side. Turn only once during cooking.
While burgers are cooking, lightly butter and toast 6 buns.
To assemble and serve: Place 1 patty on each bun bottom and top with a generous scoop of corn/onion/cheese mixture. Add bun top and serve with extra lime wedges