And even if you go to those extremes, the biggest nay sayer says the cost of the design flaw will require you to double the number of decoders, which hardly sounds like a big deal to me.
So you either need (almost) double the number of full decoders, or a length decode and a bunch of shifters to get each decoder the right input bits (which get larger the wider the front end is. The 8th instruction can be at one of 7 possible offsets)