OK - in that case you can run that from the launcher without running Steam. So if you buy direct from Frontier you can run both accounts from one installation of the game on your computer - just by copying and renaming the EDLaunch.exe file (the launcher) - everything else stays the same. That is how I run my old Steam version, the newer one has to be run via Steam.
So that is one option - the other of course is the create a new Steam account and buy the cut-price offer and hope it validates with no issues. As I say I have no experience of running two Steam accounts of ED through Steam - have you thought of asking in the Steam forums if there are any drawbacks?