help using a pickbox to place blocks

I have seen this done in the past at other firms. I am trying to insert a block on a wall using only a pickbox (one step). I am fairly new to lisp routines. I can get the block to insert fine, but I then am having trouble with the rotation. I would like the pickbox to determine the rotation automatically based off of the side of the line I pick, I currently have it asking for the rotation. If I pick on top of a line, the block faces up, if I pick the bottom, the block faces down.

Is this what you mean .... ?

(defun c:Test (/ p d)
 (vl-load-com)
;;; Tharwat 11.04.2012 ;;;
 (if (and (setq p (entsel "\n Select a line :"))
          (eq (cdr (assoc 0 (entget (car p)))) "LINE")
     )
   (command "_.-insert"
            <lockname>
            (vlax-curve-getclosestpointto (car p) (cadr p))
            ""
            ""
            ""
   )
 )
 (initget "Yes No")
 (if (eq (setq d (getkword "\n Agree with this direction [Yes/No] :"))
         "No"
     )
   (vla-put-rotation
     (vlax-ename->vla-object (entlast))
     (+ (/ pi 2.)
        (angle (cdr (assoc 10 (entget (car p))))
               (cdr (assoc 11 (entget (car p))))
        )
     )
   )
 )
 (princ)
)

This may help:

http://lee-mac.com/autoblockbreak.html

i think that is close. where do i place my block name in the code? "E-Po Duplex Wall"

Easiest way only 1 pick do not need a direction been doing this for years placing blocks on walls you just pick what is known as left side this way you always know which way is the inside. You get used to picking the wrong side, the right, when placing on a TOP line. The sides again top & bottom, left,right are both left picks.

replace with your block name its just a typo no B