Coda, OK I see.
Unfortunately, building up the grip always involves adding weight, but at least the weight is added to the handle so it doesn't increase the swingweight nearly as much as if the weight was added higher up in the frame. Maybe you can try using a heat shrink sleeve just to see how it feels for you (retains feel of the bevels better than adding overgrips does). It will definitely add some weight (~0.6 oz.) but seeing how the AK90 starts off pretty light, the increase in static and swing weight may be acceptable to you. If it doesn't work for you, you could always cut the heat shrink sleeve off.
Good luck.