Maybe use an actual network filesystem (NFS/Samba/whatever), and then throttle/shape the network traffic however you like (lots of suggestions upthread).

You could probably do it over a loopback device on the same machine if you don't have a network handy.

This has done wonders to show me just how buggy iTunes is, simply by trying to store all of my media on a remote machine.

Hm, I should add these mp3s to my library. Drag, drop, make coffee, hit the bathroom, chat with the QA guy, come back, read some HN comments, hey, it's done.

Can you move IO onto another thread, or use asynchronous/non-blocking methods? Blocking IO should never be done on your UI thread.

That's what I'd like to do, but there are non-obvious cases that I could have missed, e.g. seemingly innocent system calls, observers/event callbacks.

Also, when you make I/O truly async, you need to ensure UI behaves sanely while slow I/O happens in the background.

Use a USB stick?

In this same thinking there are still some USB 1.1 hubs out there too. This should give you a VERY slow drive for a decent price. As an example:

http://www.amazon.com/Ho97958-Usb-1-1-Slim-4-Port/dp/B00030N...

OS is too good at caching reads, so tests are not repeatable.