you should email kryptonite and ask them to get your second lock keyed alike. they will do it a for a few extra bucks.

however, they cannot key all locks alike. for example the new york std ulock has a different cylinder than both the Evolution and Fahgettaboudit and cannot be keyed alike. i tried to get all my locks keyed alike, but they were not tryin to hear that.

i have a evo mini, and i had it keyed like my evo disc lock. so i can use the mini on the frame and rear wheel and supplement that with a chain that is locked with the evo disc lock, with only one key. i would argue that this setup is more secure than the "maximum" security scenario involving the fancy locksmith padlock and cable discussed in the OP.

any dude with a grinder wins all. but in my scenario if a guy has a bottle jack to bust the U, he will also need another tool to snip the chain. like sheldon says, you want to force the criminal to have two different tools. and if i use the cable like the OP the bad guy will need a far less substantial snipping device. and he wouldnt care what sort of fancy padlock you have when he snipped the cable.