Some of the 500 series are singlepilot capable without having a waiver. A few of the 550's are as well, The sp capable 550's with no waiver had a lowered gross weight (12500 instead of 14800)
The rest can get a waiver that must be renewed every twelve months and is model specific, meaning that if you hold a waiver on a Bravo it is only good for a Bravo.
Been a few years since I held the sp waiver but 99% of the 550's and 560's out there come equipped for the waiver. If memory serves the only requirements are the gear handle on the left side, and a transponder ident button on the yoke. Basically the only ones not sp waivable would have been special order aircraft with changes to the basic factory equipment (deleting standard items) which you almost never see.
I was told by the cessna folks that they intended that the XL be sp also but that the FAA would not allow it because you could not easily see the right wingtip from the left seat.
The sp ride is pretty simple, just a normal ride with no F/O. The intial SP waiver MUST be done in the airplane, then any recurrents can be done in the sim. Also anybody on the sp waiver has a few different rules as far as OXY requirements etc.,, Mainly common sense stuff.
The entire 500 family is very easy to fly sp.
Hope this helps.