Vista - Invariant Stroke Thickness in WPF

I am attempting to produce a simple CAD engine using WPF. So far it has
produced very pleasing results and I have a working user control that
harnesses the technology. I render to a Canvas, which is then hosted onto my
user control using the ElementHost.

I have however run into a slight issue when it comes to implementing
Invariant Stroke Thickness. By this I mean that when I zoom in and out I wish
for the line thickness of my UIElements (Lines/Ellipses/Polygon/Text etc) to
remain the same rather than scaling. To Zoom, Pan and Rotate I am setting the
Canvas.RenderTransform() property to a Matrix that has been Scaled,
Transformed and Rotated accordingly. This allows all the movements I require
around the 2D space and has the benefit of making it easy to obtain the
actual co-ordinate if a user-scale other than pixels is used, such as mm, as
the matrix can be inverted. It does however have the downside that when the
image is scaled for a Zoom all the elements also Scale in thickness.

What I am after is someway to keep the Element thickness constant regardless
of the scale. I have found that this can be done on the Path UIElement as you
can apply a scale to this which does not alter its thickness but makes the
element bigger on screen, therefore giving the same affect as scaling.
However this appears to only be possible for the Path element and not Line/
Ellipse/ Polygon/Text etc. I would prefer to use the built in Elements than
attempt to replicate them using a Path if possible. I would also like to
avoid redrawing every element when the scale is changed as this proves to be
very slow and gives no benefits over using GDI. Likewise editing each
element’s stroke thickness when the scale is changed could also prove to be a
slow process.

Is there anyway way to assign an element’s stroke thickness as invariant or
a preferred way of Zooming that prevents the thickness from scaling?