Clicking "Show Details" in the choose language dialog will show a
config-panel as built below.
(module config-panel mzscheme
  (require (lib "")
           (lib "" "mred")
  (provide attach-config-panel!)
  ;; Consume the parent panel and the super-class's settings-get/set
  ;; procedure, and (1) add a new panel for ACL2 options, and
  ;; (2) produce a new settings-get/set procedure.
  (define (attach-config-panel! parent super-param)
    (let ([vp (new group-box-panel% 
                   [parent parent]
                   [label "ACL2 Options"]
                   [alignment '(left center)])])
      (let* ([admit-before-run-cb
              (new check-box%
                   [label "Admit Definitions Before Run"]
                   [parent vp]
                   [value (get-admit-before-run?)]
                    (lambda (this e)
                      (set-admit-before-run? (send this get-value)))])]
             ;; The layout of this field and the button isn't stellar...
              (new text-field%
                   [label "ACL2 Location"]
                   [parent vp]
                   [enabled #f] ;; can only change via the button below.
                   [min-width 400]
                   #;[init-value (path->string (get-acl2-location))])]
             [hp (new horizontal-pane%
                      [parent vp]
                      [alignment '(center center)])]
              (new button%
                   [label "Change ACL2 Location"]
                   [parent hp]
                    (lambda (b e)
                      (cond [(find-acl2 #f)
                             => (lambda (new-path)
                                  (send acl2-location-text
                                        set-value (path->string new-path)))]
                            [else (void)]))])])
        ;; HACK -- there must be a better way to do this.
        ;; Remove some of the (inapplicable) `simple-settings' from view:
        (send (car (send parent get-children))
              ; the receiver here is the vertical panel that contains three
              ; group-box-panel%'s
              ; (Input Syntax, Dynamic Properties, Output Syntax)
              (lambda (children)
                (let ([input-options (car children)]
                      [output-options (caddr children)])
                  (remq input-options (remq output-options children)))))
           (cons (make-acl2-settings (send acl2-location-text get-value)
                                     (send admit-before-run-cb get-value))
           (super-param (cdr settings))
           (let ([a (car settings)])
             (send admit-before-run-cb set-value
                   (acl2-settings-admit-before-run? a))
             (send acl2-location-text set-value
                   (acl2-settings-acl2-loc a)))]))))