Desert Racer, That is actually the best way of doing it. I presume any variation of that method will work as long as one can get the wheel axle, swing arm pivot and front sprocket bolt lined up. Like pulling the swing arm up towards the frame with a tie down ratchet? Also important to spin the wheel and allow for the shortest part of the chain.
The OP still doesn't have an answer to his question and I agree with him, it's not really practical to measure the slack to 50mm and hitting the swing arm before you get to 50mm. I normally just adjust it until it hits the swing arm easily.

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2014 XT660Z - Barrett pipe, DNA stage1.5, Barkbuster hand guards and handlebars, Pivot pegs, Teknik suspension, Guard-it engine protector combo, B&B rear rack, Trax topbox.