I own every model of the Otz. BTW they changed from Oetzi300 to OTZ this last month. The Brogan is the one you will have the most trouble with. If you take the insole out there are holes cut into the footbed. This is to allow the shoe to flex. It is very uncomfortable to stand on those holes though. The 300GMS and the SuperSlick don't have any holes and are completely smooth. If you wear socks you can walk on the footbed just fine. I don't have any irritation from the stitching. They don't even bother me all that much when I am barefoot. If you really need to make a insole then I would suggest this. I did it with my pair of Low Leather and it worked.
Step One: Buy some of this cork board.http://www.amazon.com/gp/product/B002M78G0K/ref=oh_o00_s00_i00_details
Step Two. Trace around your insole
Step Three: Cut the insole out a little larger then the tracing.
Step Four: Use a Dremel, sand paper, or scissors to trim off the excess to make sure you get a good fit.
It is easier to cut it a little larger in step three and slowly shave off excess then it is to cut it to size the first time. You get a more accurate fit that way.
I can get two insoles per sheet. So you should be able to get 8 individual insoles from that package of cork board.
Sometimes you have to trim the excess thread that they use to sew the upper and sole together. I notice sometimes there is a little slack left over. I can't wear any of them with the footbeds. The initial heal rise hurts my foot. How long did it take for you to flatten out the insole? What do you think about all of the styles? Also what do you think of the Super-Slick? What color did you get? I ordered the Blue Suede pair. I really like them. Probably my favorite pair of Otz yet. I just got a white leather pair of Super Slick as well. They should be here Monday. Why do you not like the insole with the 300GMS? Does it cause you to slip in the heel with it in the shoe?
In the future they are developing a minimalist cork footbed. Not sure when it will be out. It should be very similar to the cork insoles they have now just thinner and completely flat heel drop.
Within the next few weeks I should have a HUGE review on OTZ. I am combining all of the shoes I own in to one huge mega review and guide. I want to be able to lay out which shoes work best for minimalist enthusiasts. I think the some of the shoes work better then others.