type CustomNativeType struct {
	reflect.Type
}

func (t *CustomNativeType) FieldByName(name string) (reflect.StructField, bool) {
	name = strcase.ToPascal(name)
	return t.Type.FieldByName(name)
}

type Foo struct {
	MyField string
}

func main() {
	fooType := &CustomNativeType{Type: reflect.TypeOf(Foo{})}

	env, err := cel.NewEnv(
		ext.NativeTypes(fooType),
		cel.Variable("foo", cel.ObjectType("package.Foo")),
	)
	if err != nil {
		panic(err)
	}

	// Evaluate "foo.my_field"
}