I don't know how to do it with code since I haven't worked with Episerver.Forms, but since they are just blocks, you should be able to uncheck the "Available in edit view" option in Admin.

Excellent, this worked. I tried going about it with code first but without success hehe

Just remember that you will need to do this in all envirnoments(test/stage/prod) so it's better to do it with code, but I don't know how/if it's possible right now.

Yeah thats why i wanted to do it with code in the first place.. but this is better then not being able to disable them at all :) 

This should work

var contentTypeRepository = ServiceLocator.Current.GetInstance<IContentTypeRepository>();
var type = contentTypeRepository.Load(typeof(TextareaElementBlock));
type = (ContentType)type.CreateWritableClone();
type.IsAvailable = false;
contentTypeRepository.Save(type);

Great! Thanks Yauheni :)