For a wealth of knowledge regarding David Gilmour's tones, check out:
http://www.gilmourish.com/
There is not Axe-Fx specific content on this site, but there is a lot of information regarding the actual amp, effects, and settings that David has used for most of his most memorable tones, including (of course), Comfortably Numb circa Pulse.
I have not yet personally created such as patch on the Axe-Fx (as others have mentioned, it is on my list of things to do), but being a huge fan of Gilmour, I can offer a little advice...
Playing a Strat will get you in the rough ballpark, but to really get close to David's later tones (Red Strat era, before he revisits his Black Strat for his latest solo recordings and most recent live work), you'll really need his EMG set. EMG's do not sound exactly like traditional Strat single coils and his higher gain tones make use of the additional active controls and have a large impact on his tone. I personally prefer his tones circa Animals and The Final Cut, as I prefer the sound of his Black Strat, but I don't think that David has ever created a tone that is less than incredible.
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Just keep in mind that, depending on what guitar and pick-ups you are using, and whether or not you are dialing this tone in for yourself or someone else is (with perhaps different guitar/pickup combinations) that there may be need for a fair amount of adjustment.
Second, keep in mind that David plays LOUD. Set up your patches so that the master volumes are high and the virtual power stages are sweating a bit.
Bjorn's site should cover the specifics of gear and how to dial. Obviously, you'll have to tweak a bit, but this should get you close.
Best of luck!
-Matt