Those bezier handles shown are basically tan snaps in MoI for a second point on the curve.. To do this with polylines you would have to seperate them, then you could run rebuild to make the line have 4 points instead of 2. Then, drag the inner point around. If you wanted the opposing point to remain untouched, you would rebuld with 5 points, to get a point seperating the 2 inner points. MoI bezier handles.