Well, after monkeying around with it, this is what I'd use:
awk '{ print; system("sleep 0") }' edscript | tee /dev/tty | ed
or, without tee:
awk '{ print >"/dev/stderr"; print | "ed"; system("sleep 0") }' edscript
If print >"/dev/stderr" doesn't work on your system you could use print | "cat >&2".
With gnu sed:
sed -u -n -e 'p;w /dev/stderr' -e 's|.*|date|e' edscript | ed
Another way that works just as well:
Use split to split your edscript on each line:
split -l1 edscript
this will produce pieces like xaa, xab...xah.
You could then use the pieces like this:
for i in x*; do awk '{ print >"/dev/stderr"; print }' $i; done | ed
or
for i in x*; do sed -n -e 'p;w /dev/stderr' $i; done | ed
to get the expected result. Then you rm x*...