Heading to El Capitan I thought it would be easier to descend the knuckle to the east of the drainage the author describes(towards the left when facing El Capitan). I descended the knuckle until the knuckle ended and about three major drainages come together. If you descend the knuckle you should traverse the drainage and move towards the right-side cliff a little before this point. I continued to follow the drainage further down before climbing back up...I knew I was going way too far when I started to lose sight of Guadalupe so I cut back up El Capitan from the east. All in all I lost about 30 minutes
I think you could follow the drainage all the way down to El Capitan Trail. It would be a little steeper than the climb up to the Guadalupe Trail and it looks like there's 100 or so feet that are just a bit shy of being technical so I wouldn't recommend trying it on your first summit attempt.
I agree with the author that El Capitan's northern "peak" looks at least as high as the southernmost edge, but the topo maps show the southern edge as being higher. Anyways, there's a sign-in book at the southern edge so it's definitely worth the extra 10 minutes or so to meander all the way to the south. I was the first person to sign in over 4 months, so it looks like few people make it all the way.
Bring tons of water! I had over a gallon and drank it all before I even started back down the Guadalupe Peak Trail.
Last month I climbed Guadalupe Peak with some friends and we decided to bushwhack to El Capitan. I searched for info from Guadalupe Peak and used this post to inform our hike. Just wanted to say thanks for the great info. You can read about our approach here: http://wp.me/p4kzRW-2O My post also includes a photo from Guadalupe Peak of our approach that others in the future may find useful.