For my Helles, I use 50% Pils, 42% 2 row pale, and 8% Carahell; included in the 2 row portion, I use a quarter pound per 5 gallons of Platinumswaen Sauermalz. It's not the same as adding sauergut, but it is my work around instead of having a sauergut reactor actively maintained. Perhaps it is all in my head, but I like my helles. Sometimes I will sub in some light munich for the carahell, as well, just to give it a little more bready character.
Cheers!