AutoCAD Dynamic Blocks :: Stretching Multiple Lines By A Different Amount

I'm looking at a block which has multiple visibility states, 2 of which show a beam as a side elevation, where the beam can be stretched to give a length. This works well.

But I'd like to be able to have the beam stretching so the bottom flange of the beam can stretch relative to the top to give an angle to the beam end, and also have the lines representing the flanges (whose position will vary depending on the steel size) can also be stretched to give a neat cutoff.

Stretching the bottom of the bottom flange is easy, but I can't figure out how to stretch the inner lines? They would have to be moved a proportion of the distance which will vary between beam sizes/flange thicknesses, so putting in a fixed multiplication factor won't work. The mathematics to set a multiplication factor based on other elements of the dynamic block is easy, but is it possible to have such implemented on a varying basis?

Elevation showing what I want to do, and the block itself attached.