UserData nesting for external types

[IcyTv]

Hi, I'm currently having the following problem: I have external dependent types, something like:

struct Vec3 {}
struct Mat3 {
    x_axis: Vec3;
    y_axis: Vec3;
    z_axis: Vec3;
}

from an external crate.
I now want to bind Mat3 into the Lua context. To do this I (have to) use the rust "newtype" pattern, so:

struct LuaVec3(Vec3);
impl UserData for LuaVec3 {...}
struct LuaMat3(Mat3);
impl UserData for LuaMat3 {...}

and implement the UserData for those.
If I now, however, write an accessor for one of the axis for Lua, I have to wrap the resulting Value in my crate-local files. This leads (because of the ownership) to a copied Object in Lua and if I edit that, the original axis (obviously) doesn't get changed...

The only 2 options I see to circumvent this is to, either reimplement these types in my crate (not something I'm very keen on) or modify the original (glam) crate to have all the external types implement UserData.
Is there something I'm missing, i.e. a way to circumvent the orphan rules that gives me the ability to retain ownership of the object with Mat3? Or implementing UserData for the references? Or have a reference wrapper (how would that work?)?

Your help would be much appreciated.