How to attach a wire to something small and conductive (< 5 mm connection area)
You can get conductive epoxy (contains silver, silver coated copper, or silver coated nickel) that would bond nicely to the anodized aluminum and to the plastic. It is a bit expensive but you sound like you don't need much per assembly. They come as one part and two part mixtures. Two parts cure faster although an oven typically helps speed things up for either kind.

Examples:


MG Chemicals 8331
Ablestik 56C
Master Bond EP77M-F