PE 5548 standalone & PE 5548 stack connection via 10G SPF+

I simply do not have enough 10G fibre ports on my core switch (AT x908)

I have one left available port which connects to local PE 5548 (with 2 x FTLX8571D3BCL)

But in remote building (with 10G fibre cable between buildings) I have a stack of PE5548 (with its own HDMI stack cable)

How would I go about configuring "standalone" PE 5548 with remote stack PE 5548 using 10G fibre between them?

AT x908 --> standalone PE 5548 --> 2 member stack PE 5548

Thanks

Seb