Restrict features weights in GradientBoostingClassifier

Question

I am trying to create a classifier from a dataset of ~30 features, using sklearn's GradientBoostingClassifier, with 100 estimators and max_depth=3. When I look at the feature importance I see that 2 features catches ~90% of the importance. Is there a way to restrict the maximal importance of a feature? Of course a loss increase will be necessary.