Custom Choice Field SharePoint BCS

Scenario: It's always represented out of the box with BCS. I would like to do is to customize the New and EditForms to allow aDropDown in one of my fields.

I've tried: Creating a custom field based on SPFieldChoide(tested in a custom list and it works just fine) and through the BCS config XML file (.bdcm)  added the propertySPCustomFieldType to the field I want to get customized.

Error: I can open ReadItem/NewForm/EditForm pages and custom field renders just fine yet it throws an error while opening the ReadList page

Error while executing web part: System.NotSupportedException: Method 'GetFieldAttributeValue' is not supported on BiConvenioGrupoChoiceField for external lists.
at Microsoft.SharePoint.SPExternalList.ThrowNotSupportedExceptionForMethod(String sMethodName, Type typeThrowing)
at Microsoft.SharePoint.SPFieldChoice.get_Sortable()
at Microsoft.SharePoint.SPField.AnnotateField(XmlNode fieldRefNode)
at Microsoft.SharePoint.WebPartPages.XsltListViewWebPart.AddInFieldSchema(XmlNodeList fieldRefNodes, SPList list)
at Microsoft.SharePoint.WebPartPages.XsltListViewWebPart.AddInTypeInfoIntoViewXml(XmlNode viewXml)
at Microsoft.SharePoint.WebPartPages.XsltListViewWebPart.ModifyXsltArgumentList(ArgumentClassWrapper argList)
at Microsoft.SharePoint.WebPartPages.DataFormWebPart.PrepareAndPerformTransform(Boolean bDeferExecuteTransform)

PS: Everything was and has to be done programmatically i.e. through VisualStudio so in the end I'll have a .wsp that I can deploy and install it all.