It was impossible in vanilla, but with the free Extended Cut DLC, which I heartily recommend, the requirement was lowered to 3100 EMS, which can be attained without multiplayer.
That doesn't mean it's easy, though. You have to do a nearly spotless run of the entire trilogy to achieve this. Some advice:
I don't think you have enough to be able to get the best variation of the red ending. How are your war assets currently distributed?
I'm at 2360 now and there is nothing left to gain.
I'm at the Invasion of the Illusive Man now.
I don't play ME1 because of the lack of controller support so a big number of my team is automatically dead. I use mods in ME2 and 3 to unlock console versions of the games but can't seem to get it to work on ME1.
Tali and Miranda are dead so no Geth fleet. The Geth fleet would easily get my 3100 too.
It sucks because my rep has been maxed out forever but it doesn't help hardly anything important.
I saved Earth last game at 1995 EMS so I'm curious what 2360 will get.
Would love to see the synth option opened up.
It sucks finishing the game at level 63 and not getting a good ending.
ME1 doesn't affect the series too much because ME3 came out before ME1 was ported to PS3, and BioWare didn't want to disadvantage too many players.The choices you make in ME1 are not necessarily good or bad, but will change the context somewhat in ME3 missions. For instance:
You'll miss out on Wrex for skipping ME1, but you don't lose too many war assets for that. In fact, Wreav is a lot dumber than Wrex, which means you can get more war assets out of him if you play your hand right.
If you want to skip Mass Effect 1, you can always just download someone else's save file from http://masseffectsaves.com/ to get a more complete playthrough.
You can boost your EMS by using the Mini game at N7 HQ. Login with the same credentials you use for Origin and then choose "Galaxy at War"
Here you can play the Mini Game that pushes the "Readiness Rating" up, exactly like playing MP would do.
For the EMS, you can obtain max 3750 EMS in a game without any DLC's, so reaching the 3100 EMS needed if you have the "Extended Cut" installed is possible.
To be honest I always found it to easy to get the EMS score you need after the EC was released, but I also never lost someone (exept Wrex) in the first and second game.
Also important to note you have to achieve the required EMS before going to Cronos Station. That's when you're locked in.
