I didn't want to make an unreadably long comment by trying to solve every detail.
But GPL just adds that the source be made available to any recipient of code you used. That's pretty easy to arrange because even a link satisfies it.
If copilot can be made to spit out attribution, then it can spit out links at the same time.
Another idea is copilot could be changed to only include code where the authors opted in to an aggregate credit where your new program only has to declare that it used copilot and a link to copilot's training set along with your programs source, without trying to itemize each bit of output.
There could also be other versions of copilot that includes other code under other terms, like pure MIT or PD code where the original author already explicitly granted usage with no terms, or paid commercial code where github paid the authors to be able to include code to be used in this way and maybe with terms where the end user does not have to re-share.
The "link" necessary here would be a link to the full source code of the software developed with the use of copilot, distributed with every copy of said software
