Calculating M Values To 3D Length

Trying to figure out how to calculate M values using 3D distance. This doesn’t seem to be as straight forward as expected with ArcMap so would like to see if we are missing something. Google unfortunatly did not turn up much on this topic.

Here are some things we have tried:

1) In an edit session, right clicking the line and "Route Measure Editing" -> "Set As Distance". This ignores Z values and only calculates a 2D distance.
2) Add an attribute and "Calculate Geometry". This allows to calculate the "3D length", but only for the total length, not all the vertices in-between. Also requires the feature class to be in a projected coordinate system, which makes sense, but would be nice to calculate on the fly.
3) Using 3D Analyst there appears to be tools that will set the Ms based off draping over a DEM (did not explore this much). We would like to use the higher precision Z values for the calculations than a low resolution DEM. Also sometimes our Z values are for buried pipe, so the surface elevations are not what we want.
4) Using arcpy, looping all the vertices and using distanceTo() to set the Ms. This is only a 2D distance.
5) Using arcpy, looping all the vertices and manually calculating the 3D distance to set the Ms. This is the only option that works for us at this point.

Is there something we are missing? This seems like it should be a simple calculation so hoping we are just overlooking something.

Thanks a lot for any help.