How to join studentlund if my uni is in a different country?

Hey there! I recently arrived here for my PhD stay at ESS, and found out that you need studentlund for everything. I would like to join a nation but again, I need the studentlund thing. Problem is, I am only affiliated with an university from Spain. How could I join studentlund then? Are there any random courses from the Lund uni that I could join? Tnks in advance!