As if there isn't enough bass in this world, your guy has to come along and add even MORE?!?!? There is a way to "properly" double-track an instrument or a voice. It's called "playing tight and in tune", and it doesn't sound like he's doing that. Is this a fretless bass? Is he checking his tuning before he does the 2nd track? Are you using a DAW so that you might have access to one of many plug-ins that will help "correct" the "pitchiness issue" (that's what's causing the 'chorusing'). Has he not been able to use a decent digital delay stomp box that can be set at around 30-40 msec of delay to generate the desired effect? Bsaically, if he's gonna go the "natural" way and really play the doubled track, he needs to practice, practice, practice until it's TIGHT!

WHY?

What is the purpose?

Dont get me wrong ...it can be done. I'm a very good bass player and it would require a LOT of work to get the tracks perfect with each other. If theres no truly eye-opening purpose to this then why do it at all???

Take two,three, even four tracks of the same part. Each mic'd differently...different amp...different part of the room...direct line...anything....at the mix you have a LOT of control to do anything you might want as far as an effect....and they'll be IN TUNE and IN TIME.

Quite a concept.

Davedog has it!!!

Record the cabinet (MIC) and DI on 2 seperate tracks, and play with it.

I ussually try to do what the others have suggested, The old amp, DI , and Sansamp , thats ussually lots. Although I have heard of Bass players re do int there parts in a higher ocatve, of course this depends on the band and the music, but it might be something fun to try .

Bass guitar to DI (SansAmp or whatever) then from DI to amp/speaker cabinet. And mic your speaker cabinet up close (but not too close). Now you will have 2 seperate tracks, both sounding way different, and they should mix nicely like this.
As stated above, record both tracks at the same time.
Good luck
In my past---When I double tracked the bass guitar it sounded awfull and muddy too. So no more multi-tracking bass for me

Thanks everyone.

Now I can tell him that no one double tracks bass. I have been doing the DI and amp thing and it does sound good.

And I as mentioned earlier it does sound good with an overdriven bass, especially when played in different octaves. Good for a freak out section or under a solo.