When initiating the call for fire, "danger close" is given in the warning order transmission. If it's the establishment of an FPF, the FDC is notified in the target description transmission.
A danger close mission, as in an FPF, is first adjusted onto target using the gun that's closest to the target (as in which gun in the section and how it relates to the gun line attitude in corelation to the target). In addition, all rounds fired during the adjustment phase are either WP or ground burst illumination. Once the F.O.s declare the round is adjusted, an HE round with the fuse set to "delayed" is fired just to confirm.
Now that the closest gun has been adjusted and deemed safe, all other guns of that particular section are given their respective data based off of the adjusting piece's deflection and elevation. The exception to this would be if the mission called for a converged sheaf, which only differs in that each gun fires a confirming round.
It sounds pretty "mickey mouse," but you have to consider that you are dropping exploding HE rounds within yards of friendlies, besides the whole process, when conducted by a competent FDC, can be accomplished inside of 5-minutes.
As I'm typing this I believe I'm on my 6th or 7th beer, so if I f'ed up, somebody please correct me. Really though, it's all pretty simple.