We need to know some more details about the content of the data and the destination in your webpages.
If you write some Actionscript, you can easily make HTTP requests to your server, with the data packaged into whatever size chunks are convenient. You will get a response to each request, so you can handle the data as it flows in. This will allow you to "throttle" (control the speed) of data flow.
The server will have to know to send the data packaged into the chunks that you want.
If you give more details about your application, we can answer in more detail.
Here's an interesting link http://www.flexafterdark.com/docs/Flex-HttpService