Are you certain the entire surface is solid? I've got an IKEA desktop, and it's got solid wood around the edges, but the center is a hollow-core/cardboard honeycomb type of construction. The wood in mine (probably particle board) extends in about 2" (~5cm) but then the rest is that hollow-core construction. Tapping on the desktop with a knuckle makes a distinctly "solid" sound near the edges, and a "hollow" sound anywhere else. With my desktop, there is NO WAY I'd be able to support 15Kg from the bottom of it. If yours is hollow anywhere, it won't either!
I also purchased a sit/stand desk leg setup from IKEA, but the top I purchased wasn't "officially" supposed to go with it. I was able to attach the legs to the wood in the top, but I've attached nothing in the center.
To accommodate the movement, I've got my tower CPU sitting on the floor next to the desk and long USB & video cables (10' IIRC - my CPU isn't right next to the desk) running to the desktop. Along the bottom edge of the desk, I installed some cup hooks along the edge into the solid wood for cable management, and I've got the cables run to the side of the desk where they drop down to the floor. When the desk is lowered to the sitting position, I've got a bit of a tangle of video cables, but I've got enough slack that I can raise it to a standing position without pulling on anything.
I looked long and hard to find a power strip with a long cord and with mounting slots on the back near the edge (not down the middle). I used the mounting slots to put it on screws at the edge of the desktop (into the solid wood), then all the monitors & other desktop accessories plug into the power strip with cords neatly bundled up under the desk. Then I've got the one power cord running to the ground where it plugs into the UPS. The cord is long enough to accommodate the vertical movement, as well.
At some point, I'll add another hook to hold the cables to the table bottom, then put a weight on each cable between the last two hooks. This will force the cables to be in a "droop" between these two hooks, yet allow it to slide as I raise the desktop. This should tidy up the rat's nest of cable while still allowing them to move. I just haven't been motivated enough to mess with it yet. :)