I have a Samsung Galaxy Mini (GT-S5570) with Froyo (Build FROYO.XWKE3 in case this is relevant). When scrolling a list it allows the list to scroll past the end, and then slowly scrolls it back. This prevents me from using the technique I've used on other Android devices where I flick a list and let it hit the end in order to select an item from the last screen (it takes about a second for the position of items to settle down, which is really annoying, and I'm not accurate enough to select them while they're moving). Is there any way (short of a custom ROM) of disabling this behaviour?
No - as you've correctly ascertained, a custom ROM is most likely your best bet. Also, the bounce effect is a Samsung "feature" - by default Android uses the glow effect to indicate the end of a list. I'm also unsure if this is a Froyo only feature, because IIRC, one of the UI updates was the glow effect, which Samsung did incorporate into their later ROM releases.