First off, you'll need to create a shortcut key to "Relocate Origin", (which should be in the "coords" toolbar, but isn't):
Right-click on the blank space in any toolbar. When the window pops up, change to "keyboard" tab. Change "Category" to "modes"; Find "coord system" & create a key - let's say Shift-L - for "Relocate origin".
Well, basically, that's it! You've created a "from" snap equivalent. Now to actually use it:
1. Create a Rectangle 20 x 20 units
2. Start a polyline. Start from lower right corner of the rectangle. Let's say you want the second point @ distance 5,5 from the upper right corner. (This is where you'd normally use the "from" snap in Autocad).
3. Press Shift-L (The key you created for "relocate Origin, remember. Click on the Upper Right vertex of the rectangle). Type @5,5.
As you can see, this automatically sets a point for the pline at (dist.) 5,5 from the selected vertex. And, of course, you can use it with centers, midpoints, etc.
[Edit: ALt-L is already the key for "Close Polyline"; changed it to shift-L. Looks like nobody was interested in this tip
. Anyway -being such a wonderful person - added screenshot to show what I meant. ]