The short answer is no.
When you initially pick up the receiver (off-hook), the dial tone is being generated by the GXW (assuming the extension from which you are dialing is registered)… Dialing any number after that is the dial string that is expected to be delivered by the GXW to the SIP device to which it is connected. It is essentially 1-stage dialing.
The device to which the GXW is connected is the one, that upon seeing the string from the GXW would need to provide the secondary dial tone and then you could enter in the other string (2-stage dialing).
In most of the systems today, if a prefix is used (9, 8 or other), it is typically used to define the path to the needed outbound route trunk (route) or a holdover from a prior system where users are still in the habit of dialing without the prefix. .