Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)

"I am working on the assumption that I will ask the check-in desk at LAX to only check my bag through to LHR."

No, you're working on the assumption that Virgin will honor your request to short-check your bag. If all of your flights are on a single ticket, that's a bad assumption, unless you have an overnight connection at LHR.

Suggest you check the FT Virgin Atlantic forum to see if there's any discussion there of VS's short-checking policies.

Note that if your flight to DUB had been booked on EI's LGW-DUB service, you would not have a checked-baggage issue, as airlines generally do not transport baggage to a co-terminal for a connecting flight; that is the passenger's responsibility.