1) To deliver downloads on-the-fly - read them in using a loop from a local file and then print that loop content as it goes. If you are giving a low download speed then just add in some sleep() commands within the loop at appropriate points to slow it down.

2) To use a slower server for slower downloads - this option may make the most real sense - get hold of a cheap hosting account with unmetered bandwidth and use that.

3) Apache can be configured to limit the rate, but I've not done it before.

Are there other ways to do it, mechanically, so to speak? Such as two servers?