I have found a very good solution for laptops or ultrabooks that do not have a Kensington type of locking slot anymore:
J-Plug Lock from Multplx.
I have ordered the J-Plug directly with the manufacturer in the UK as there are basically no stores/distributors in the EU yet.
I assume that the J-Plug was initially made for lage scale use to prevent demo devices from theft (e.g.: exhibitions, large sales stores, etc...).
The people at Multplx really did a great customer service job for my tiny, tiny one item order. Called me twice from the UK to Germany to handle my inquiry and the order itself.
The J-Plug (with loop) and the Tetrakey Security Tool (needed to actually lock/unlock the J-Plug from the 3.5 audio jack) arrived in less than 24 hours (UK to Germany).
J-Plug Lock: 23 GBP
Tetrakey Security Tool: 12 GBP
Shipping UK to Germany with DHL: 29 GBP
I am really very impressed by the speed this single item order was handled by Multplx.
I have of course immediately tried it and I must say: it is really what I was looking for.
If you are looking for a physcial lock for your YOGA 900+ ultrabook or any other ultrabook that does not have a Kensington lock option and DOES have a 3.5 audio jack: J-Plug Lock imho is the perfect lock.
I would suggest a small closeable (zipper) bag/pouch or the like to keep the lock in it while travelling, so you do not loose the needle bracket and/or the back cover. If the Multplx Tool (screwdriver) fits in there as well, even better :)
Here is an image of my J-Plug Lock that arrived yesterday attached to my YOGA 910s: