I would be interested in seeing a video of your screen as you use the multi point fill (MPF) command between the 2 points specified in the original post - more specifically how you are finding the location for placing each elbow "As you are running, ......" I tried a number of times (tracking and point filters) to locate the point while in the MPF command with no success. I would appreciate direction if I am doing things incorrectly.

Given that the elevation/location of the upper elbow is unknown (but could be calculated...) from the original information, there doesn't appear to be any major benefits using the MPF approach over the normal Design Line or the Design Line Trace approach illustrated.  The need to have different elbow components (short sweep and quarter bends for example) appears to be a issue when populating Design Lines.