I came up with this little routine to get a field expression using the field command. I don't know if it would be of any use to anyone (or if someone else has another way to get a field expression), but I'd thought I'd share.
(defun makefield (/ ss fieldexpr)
(command "_field"
(if (= (getvar "cmdactive") 1)
"0,0"
)
)
(setq ss (ssget "x" '((0 . "MTEXT") (10 0 0 0))))
(if ss
(progn
(setq fieldexpr (vla-fieldcode (vlax-ename->vla-object (ssname ss 0))))
(vla-erase (vlax-ename->vla-object (ssname ss 0)))
(setq ss nil)
)
(setq fieldexpr nil
ss nil
)
)
fieldexpr
)