I don't believe there is a way to disable it.
Im not a huge fan myself because if I need recently used plug ins, I will just clone them by Holding CNTRL and dragging them to a new FX bin.
With that being said.. I wouldn't go as far as wanting to disable it. its only 5 seen.
If your on a laptop (smaller screens) im sure real estate can be a concern. So I can see your point.
there might be a way to use the registry to disable it, im not sure.
Hope the bump helped
By the way, do you use the Browser of FX bins to add plug ins ?
I ask because I used to be a die hard FX bin user (the arrow/right click=add FX) but I started using the Browser a while ago and it has really grown on me. I like it.
theres a thread going on here
http://forum.cakewalk.com/TIP-Create-a-Favorites-folder-in-the-plugin-browser-m3640081.aspxHow to create a Fav's folder in the Browser, possibly someone will recommend a Registry hack (which I swear I saw somewhere) to limit the amount shown or even be able to disable it in the Registry.