Actually - I made one for my R1200R - looks just like the $60 ones vendors sell. Cost was about $5.
It's a piece of radiator screen metal (perf-metal-aluminum).. cut to fit inside the frame around the oil cooler. It just sits there, with a bit of foam tape on the back edges of it to press it against the frame.
I did cover the size of it in one of the articles I wrote for the BMW_MOA June '08 Owners News.. it's 9" x 6.25". You can find the perf-metal at any big-box home store (Lowes, Home Depot, etc.)
Here is a photo of it:

I've seen no signs the engine is running any hotter with it..