Interpolating splines - tool/cmnd?

Is there a way to interpolate "a missing spline" in C4D?
Say you have a loft-setup of , say, 5 splines gradually changing in size - which is close
to perfect, only, you need a 6th spline between spline "nr. 4" and "nr.5".
I really need the final loft shape to remain the same after adding that 6th spline - now,
is there a tool able to (based on interpolating spline 4 and 5) could generate the in-between spline?

I do have a [tedious] workaround so far...but there gotta be an easier way;

If i make my loft setup editable (>polys), i could select the generated in-betweens as points and use the plugin "polyline2spline" to generate a spline - and using this spline in my original setup. However this is by no way a
very exact method.

I'd be happy for any kinda input on this one. /tia