There are various ways it can be done. For figures that have PBMCC channels, eg V3, V4 (and most recent DAZ figures); When you have a number of morphs, that you want to inject at the same time, you can use a cr2 editor, such as  "CR2Builder" or "Cr2 Editor", to make the delta injection file. A delta injection file is essentially just a targetGeom channel, or collection of targetGeom (morph) and valueParm (FBM) channels, packaged as a pz2.

First you need to construct a template pz2 file. The template should include each actor that you need to inject into, and each actor should contain a 'channels' section. For example, to inject into the head and neck, you could use this template:

{

version
    {
    number 4.03
    }

actor BODY
    {
    channels
        {
        # Place channels below this line.

        }
    }

actor neck
    {
    channels
        {
        # Place channels below this line.

        }
    }

actor head
    {
    channels
        {
        # Place channels below this line.

        }
    }
}

Load the cr2 containing the morphs into one side of the cr2 editor, and the template into the other side. Then Drag the morphs from the cr2, and Drop them on the places indicated in the template. A pz2 file can only inject a morph into a channel that already exists in the figure (except for pmd injection). So as a last step, all the internal names of the morphs in the template must be converted to PBMCC names, eg:

PBMCC_01
PBMCC_02
etc...

---

An alternative to the above is to make a PMD injection, but they will only work in Poser, not D|S. The big advantage of PMD files is that they can create new targetGeom (morph) channels in the figure, so you are not limited to PBMCC channels, and the risk of conflict that they intale.

The py script Scene Fixer can make delta injections and REM files, but only as one morph channel per actor.

Another way to make delta injections is to use the free "Pozers Little Helper" (PLH) application. PLH can take a morphed  full body obj file and construct INJ and REM files from it, but like Scene Fixer it can only do one morph per actor.

You could use PLH or Scene Fixer to make a number of individual injections, then merge them into one file.