I know there's a way, I know I've done it (a long time) before, but I can't remember or find out how to do it!!!
var otherDomain = AppDomain.Create("Lol my memory sucks");
var myRemotableType = typeof(MyTypeThatExtendsMBRO);
var proxy = otherDomain
.CreateInstanceAndUnwrap(
type.Assembly.FullName,
type.FullName);
// how do you do this next step???
bool isProxy = IsYouIsOrIsYouAintAProxy(proxy);