I'm using a lv37 cw with crap gear and recovery here so it takes 2 shield cast for my action bar to fill up in order to cast daily.
This should not be the case for a level 60.
[update: map has been optimized for shield to hit more targets and generate more action points]
You can exit from ANY of the 8 portals back to town. Just abandon the foundry quest after killing the drow and you'll have that option.
NW-DRFH9UM67 - 40 enemies
NW-DGOQ6GCCU - 20 enemies (GF can solo with fighter's recovery daily)
Ignore the ogres
Use the teleport to get to the drow elf
there is no cooldown for cw shield
make sure it's the 1stskill you use
shield->daily->shield->daily
i personally find that double the mobs do not mean double the boxes,
so i usually just do the map with 20 mobs.
let me know if there are any bugs
just delete the quest and you can exit immediately after kill the drows