If you just want to take the Eurostar, and don't care about Paris, consider hopping on a TGV from CDG to Lille. Most of the CDG-Lille trains go to Lille Europe, the same station that the Eurostar leaves from. It's a sub-10 minute walk from Lille Flandres to Lille Europe if it goes to the other one. Takes about an hour on the TGV to Lille (so not far off the RER timings), and you're then almost an hour closer to London!