Another idea: so long as you are careful about installation, if you are putting your LED lights inside cabinets, you can probably use the hanging system holes for running your wires behind the cabinets.
Here's how I would do it:
Two people to install in this case would be a
must. Put your light into the cabinet, run the wire out the appropriate hanger hole. Tape your wire inside the cabinet
below the hanging hole. Pull the wire coming out the back of the cabinet diagonally to the side of the cabinet, gently until it is taut, and tape it on the outside of the side of the cabinet. This way, you are using the void created by the rail at the top and the lip at the bottom for the wire. By taping your wire taut along the bottom lip of the hanging hole, it won't be in the way of the bolt.
Hang your cabinet, being very careful not to pinch your wire while doing so. Make sure the wires running from your lights are free before you level and finalize the cabinet placement.
Wires can be run horizontally along the bottom lips of the back of the cabinets, and out the small holes in the corners, between the cabinets. This way, the transformer and switch can both be placed under the cabinet, behind the light rail.
Of course, some will prefer to place these inside cabinets. This will require either drilling a much larger hole, or disconnecting the plug wire from the transformer. I haven't opened mine up, so I don't know if it can be done.
In my case, my LED's are on the outside tops and bottoms of cabinets. Some, I ran after the fact, others during installation. The void behind cabinets is very handy. Because of our particular arrangement, we had to drill holes through end panels placed between cabinets, just above the bottom lip. You can see the hole, if you stick your head snug against the wall under the cabinets and look up into that space. My philosophy is if you're doing this, however, you deserve to see whatever you see.
Martine