could've used scotch, but cordial's more PG I guess. No one likes watered down scotch.
Although there is a catch, if the wastegate in your turbo is set to a very low boost at standard then running it with no aftermarket ECU should be safe, it won't be the best, but it'll be safe. I mean, if you had a TD06 25G, and the wastegate was set to 8 PSI (hypothetically speaking of course) then its no different to a standard sized turbo with a wastegate set to 8 PSI, as after it reaches this amount of pressure both turbos will bypass. In fact being a bigger turbo you might find that at lower RPM's the turbo dosen't spool up fast enough to push as much air, and thereby gives you a RICHER mixture. However this is only if your bigger turbo runs an internal wastegate that's set to a close to stock pressure... most aftermarket turbos aren't.
Bottom line, your fuel needs to match the air going in, running rich or lean is not optimal... but too lean can be dangerous.