[Serusers] Need to modify username

I am in the process of establishing a SIP-based system using SER which will allow my end users to connect to each other and to dial out to the pstn using a SIP/pstn gateway run by a provider downstream. Some of the users on my system are consultants who work on several projects at once. They would like to prefix the numbers they dial with their own arbitrary 4-digit project codes for different calls and have the accounting I send them show the project code they used for each call. Since my accounting is done downstream at the pstn gateway, and it shows the username for each call, I would like to change the username on each of the calls going out of my SER to include the project code. Then no changes would need to be made in the billing software and each call will be easy to identify as to user and project. Of course the project code would get stripped off so that just the correct uri is sent, and I have figured out how to do that using the strip function. But I am new to SER and just figuring my way through this, so I need a bit of help with the rest of it. Here is an example of what I want to set up. If user Mike wishes to call 1-111-1111 and wants to code it to project 1234, he would dial: *123411111111(a)wherever.com and the outgoing uri would be just: 11111111(a)wherever.com (this is done using strip) and the outgoing username would be: mike1234 Note: the asterisk just indicates that a project code follows. Not all users will want this feature and calls without an asterisk will be handled differently. If I can do the last part (change the outgoing username to mike1234) I'll have it cracked. It would be best to do this within SER, but I don't see a way to do it. If there is a way, please let me know. So then it seems to me that the best thing might be to use the exec_dst command to pass a set of commands to the shell would cause characters 2 through 5 of $SIP_ORURI to be appended to the end of $SIP_USER. So something like: EXPORT $SIP_USER=(characters 2-5 of $SIP_ORURI) ...... Obviously my bash-knowledge needs a bit of work here ;-) If this would work, can someone tell me the shell commands to use? Alternatively, what about calling a small executable that reads the appropriate environment variables and changes the value of $SIP_USER before returning to SER? I had at first thought this might be the simplest way to do it, but now I understand that when a program modifies an environment variable the variable returns to its original value when the child process ends. If that is correct, then SER would never see the change. Note that I'm aware that it would be easier to do this accounting on my own SER system, where I have access to the original user name. However, since the pstn gateway at the next hop does the official accounting and billing, I want the billing it produces to include the project codes, and I think the easiest way to do this is for me to modify the outgoing username. I have been working away at this, starting from zero knowledge of Linux, but I've come about as far as I can get. I would appreciate any advice. Thanks, Mike