Dynamically Create And Delete A Function At Runtime?

I'm using a 3rd party API that does asynchronous requests for me and directs response to a callback that I specify. Since my code can issue multiple requests concurrently I want some mechanism to match each response to the specific request e.g. attach a unique ID to be returned with the response. The 3rd party API does not allow me to attach any user context to the request so the only way I could figure out how to do this was to dynamically generate a callback function per request and embed the unique id in the body of that function. When the callback is invoked I can use the information to complete my handling of the response.

1) First of all if anybody has a better idea on how to achieve the above without dynamically generating script I'd be happy to hear it.2) Regardless of (1), if using my proposed method repeatedly I will be generating a lot of garbage over time, so I want to clean up after myself. Meaning, to delete the dynamic callback after it completes. Below is an example of how I wanted to do it, but it seems not to work:

Code:
function CreateDynamicCallback(callID)
{

[code]....