How to exclude Form elements from a custom FormContainerBlock and include elements for a custom FormContainerBlock?

Hi!
I have created a new class that inherits from FormContainerBlock (lets call it MyCustomFormContainerBlock).. and so far everything works great, I can use it just fine with EPi Forms.

I also needed to create a few custom ElementBlocks, which I simply did by creating a new class and inherit from whichever current implementation of a default element that fit my needs the best.. for instance:

[ContentType(GUID = "{771addcf-0174-493b-b97c-6002ef88905e}", GroupName = "MyCustomElements", Order = 2000)]
[AvailableValidatorTypes(Include = new Type[] {typeof (RequiredValidator), typeof (RegularExpressionValidator), typeof (EmailValidator), typeof (DateDDMMYYYYValidator), typeof (DateMMDDYYYYValidator), typeof (DateYYYYMMDDValidator)})]
public class MyCustomTextboxElement : TextboxElementBlock
{
[Display(
Name = "Something custom",
Order = 2999)]
 public string SomethingCustom { get; set; }
}

And I also created a controller with an action for the above Element:

public override ActionResult Index(MyCustomTextboxElementBlock currentBlock)
{
    var path = "~/Views/Shared/ElementBlocks/TextboxElementBlock.ascx";
    return PartialView(path, currentBlock);
}


Everything renders just fine, and it all works just fine with forms.. however.. I would like to be able to only show my custom elements for the MyCustomFormContainerBlock, and for the default FormContainerBlock I would like to exclude my custom elements..
is this possible?

So far I have tried to override and use AllowedTypes for the ElementsArea-property of MyCustomFormContainerBlock, but if I specify my custom elements they dont show up in the UI for some reason (the contentarea doesnt allow the user to pick any elements)