(defun c:sb (/ b2s)
(setq b2s(getstring T "Name of block(s) to select? (separate by comma) <select>"))
(if (= b2s "") (setq b2s (cdr (assoc 2 (entget (car (entsel)))))))
(sssetfirst nil (ssget "x" (list (cons 0 "INSERT") (cons 2 b2s) (cons 410 (getvar "ctab"))))))