The B100 is less than 12,500 pounds and doesn't require a type rating. If the person already has a multi rating with high performance, high altitude, and complex endorsements the "sign off" is more of an insurance issue if it is part 91. The 300 series King Air requires a type rating but the 100 and 90s do not.
The Practical Test Standards will be the same for the B100 as it would be in an Apache. The drawback is the King Air has a bunch of systems and stuff you'll be expected to demonstate knowledge about since that is the aircraft you are providing for the checkride. That sounds like a bit of overkill to take a King Air for a commercial checkride. I have quite a bit of B100 time and I can tell you some of the elements required are a handfull in it. I wouldn't want to foot the bill for the fuel either.
If you don't already have a multi-rating then the easiest way to go is to do the single commercial first. Then you only have to demonstrate commercial level knowledge and keep your headings, altitudes, airspeeds within commercial limits (+/-5 degrees, 50 feet and 5 knots) during the plain old multi ride. You will have to shoot a few approaches also to be able to fly multi instrument stuff.
I hope this helps.