[pstricks] putting a box around a pair of nodes

[John Frampton]

Dear all,

I cannot solve the following problem and would very much like
some help.

If the zero dimensional node A1 is directly above the zero dimensional
node A2, then I can easily put a box around A1 and A2 using:

   \SpecialCoor
   \psframe[nodesep=2.5ex]([angle=135]A1)([angle=-45]A2)

Each corner of the box will be a distance 2.5ex from one of the
nodes.

Is there any way to accomplish this if the points P1 and P2 are
not vertically aligned?

I have just started working my way through the Postscript
Bluebook, but I am not yet able to write my own postscript code.

Thanks,
John Frampton