I don't think this is possible by default. Perhaps you could work around it by using a constraint attribute type. As this will allow you to type in xpath. In Xpath you are able to access the enumeration values.
Ther are 2 types of enumerations
1) Mendix entity attribute of the type enumeration.
In your widget you can access the details via the MetaObject
https://apidocs.mendix.com/6/client/mendix_lib_MxMetaObject.html
var mxmetaobject = mx.meta.getEntity("MyFirstModule.Paint");
mxmetaobject.getEnumKVPairs("Color"); // { red: "Red",
// green: "Green",
// blue: "Blue" }
or directly through the mx object
https://apidocs.mendix.com/6/client/mendix_lib_MxObject.html
mxobject.getOptions("Color"); // [ "red", "green", "blue" ]
2) Widget attributes, options to configure inside your widget.
<property key="colorEnum" type="enumeration" defaultValue="xff0000">
<caption>Textcolor</caption>
<category>Appearance</category>
<description>The textcolor of the message in the widget</description>
<enumerationValues>
<enumerationValue key="xff0000">Red</enumerationValue>
<enumerationValue key="x000000">Black</enumerationValue>
<enumerationValue key="xffffff">White</enumerationValue>
</enumerationValues>
</property>
https://docs.mendix.com/refguide6/xml-reference-guide#enumeration