If this was even a remotely feasible problem with modern cryptographic hashes, DNSSEC, TLS, SSH, package management systems, most authentication systems, etc. would all be dramatically broken.
If I had this capability I wouldn't waste it on injecting javascript into web pages. I'd create forged browser upgrades and go from there.
Every website using jquery will have the real hash, so you can poison all the mirrors you like and it won't matter.
The only way to get the wrong hash onto sites is to actually publish it on the authoritative server. That's not cache poisoning, that's a malicious official version.
If I had this capability I wouldn't waste it on injecting javascript into web pages. I'd create forged browser upgrades and go from there.