What's the best filler for DIY tianeptine sodium capsules?

I'm considering using confectioner's sugar or creatine. Also, any suggestions for the best way to create a homogeneous mixure with powder? My plan is to simply tumble the tianeptine powder in a screw-top HDPE container with a measured amount of the bulk powder of choice and encapsulate the mixture. Any advice is helpful. Unless it's a snarky "Go to r/tianeptine" Haha.