At the moment I assume that there is no native way to do this, correct me if I'm wrong.
So I wrote a little script that will interpolate (not smooth) tilts of the selected points linearly:
import bpy
curve = bpy.context.object.data
# create point list
points = []
for pt in curve.splines[0].points:
if pt.select:
points.append(pt)
print(pt.tilt)
starttilt = points[0].tilt
stoptilt = points[-1].tilt
# linear interpolation
print ()
increment = (starttilt - stoptilt) / len(points)
for pt in points:
pt.tilt = starttilt - increment
increment += (starttilt - stoptilt) / len(points)
print(pt.tilt)
This will loop through the selected points and set the tilts to interpolated values between the original tilt of the first and last selected points.
Result:
