An alternative to placing a temporary origin (which I don't think I have ever done, but not saying its a bad idea) is to add a + or - to give a point relative to where the cursor currently is. Put this after your coordinate but before you hit enter.
eg. if you want a door to be 100mm from a wall intersection, with door tool active hover your cursor over the intersection, hit X, then "100+" in the tracker coordinate box, then ENTER. This will move the cursor 100mm to the right, a -(minus) will move it 100mm to the left. You can use the same technique with Y and R / D coordinates, and use it for many other situations, such as starting a wall offset from another. I think previously you had to use the "+" on the numeric keypad, but it now appears to work with "SHIFT ="