michael said:
>   In other words

move the edit field offscreen to do the insertion,
then move it back onscreen afterwards...

edit field -1,,(3000,3000)-(4000,4000),
'rem do the insertion
edit field -1,,(20,20)-(400,400),

also, for repeatedly appending to an edit field,
i recommend "fn teappend", as follows:

CLEAR LOCAL FN teappend(thefield,thetxt$)
IF thefield=0 THEN thefield=WINDOW(_efnum) 
AUTOCLIP=0 : thehandle&=TEHANDLE(thefield) 
LONG IF thehandle&
txtlgth={[thehandle&]+_telength}
CALL TESETSELECT(txtlgth,txtlgth,thehandle&)
CALL TEINSERT(@thetxt$+1,LEN(thetxt$),thehandle&)
END IF
AUTOCLIP=0
END FN

if you want to insert
rather than appending...
it's easy enough to modify 

-bowerbird