Is there a special tool to make this easier?
Here are a couple pictures of the adjuster tool from Kawasaki (part number 57001-1220).
It's not cheap at $49 (Ron Ayers part #57001-1220, or see your dealer) but it does make the job a lot easier. It's basically just a low-profile 9mm 12-point socket welded to an extension that is just the right length, with a hollow shaft so the matching screwdriver can be inserted through it.
There is also a 'board' Kawasaki valve tool that is available as a loaned tool, with a few requirements. You can read more about this option here.
It helps because there are no sockets to lose into the top-end, and it allows less work to get the adjustment correct without changing the adjuster setting while tightening the retainer nut. Many people find it easier to do the valve adjustments with it. Many just use a deep-well socket and an eyeglass screwdriver.
Kawi also sells a special feeler gauge (old part #57001-1221, new # is 57001-1553), which has the maximum and minimum clearance thicknesses on it; it gets pushed in, and when the thin end goes but the thick end won't the valves are set. For $59 shipped from Ron Ayers, you have to decide if it's worth it. A standard set of gauges from Sears costs less than $10.
Try to find gauges that are about 6" long. There is a discussion of feeler gauges at the valve adjustment Hints & Tips page.