heeheehee "rapid bladder change when running".
There are a few different things I've tried when racing with the 1.5-liter bladder size since it only lasts for a half marathon.
1) I used to race with the old Hydrobak model (http://www.amazon.com/CamelBak-HydroBak-50-Hydration-Pack/dp/B0019D9DMS/ref=pd_sim_sg_3
), which had the bladder cap opening right on the outside of the pack. At special needs I would have my rocket fuel mix in a 2-liter bottle and just open the cap and pour it in. Took a little bit of time but I wasn't fast enough to worry about it and poor enough that I didn't want to have to deal with buying a new bladder or new Camelbak...
2) I have also just had a second bladder full of rocket fuel at special needs, and did a bladder exchange--in case I didn't get it back then I'd only have to buy a new bladder rather than an entire new Camelbak. A little bit quicker than option #1.
-->so that's what you do in your original question, Julie, and it comes down to practice I guess! I can't say I practice doing this in training but I've raced with it enough that I do start to take off the Camelbak as I approach special needs...but pretty much just as you described!
3) Then there's the have an entire 2nd Camelbak + bladder at special needs which I have done lately, as it is the fastest but of course riskiest for not getting your gear back...
To get my Camelbak or bladder back after the race, I've done 2 things... at the smaller races I ask the race director or one of the head volunteers to get my gear back. For bigger races when I've been lucky enough to have a friend/sherpa, I have them stationed around special needs usually around halfway, then after I abandon the 1st Camelbak, they go and retrieve the nice sweaty thing for me.
Special needs was at the other end of the Cozumel run course though and by then it was the last race of the season and my Camelbak #1 was pretty disgusting by then so that one got to go to Camelbak heaven.
Of course I may not be so concerned with paying for Camelbaks any more in the near future if I don't get them back after a race...