You'll usually have better luck with a co-founder on board, but I've seen people get into accelerators as single founders. If you have tech. chops, there are also programs like "Hackstars" (http://www.techstars.com/hackstars) that will allow you to get into certain accelerators on technical skill alone.
I'm not aware of any accelerators that can stomach a single founder. That being said, focus on what will help your business be successful. If your business will do better without bringing a cofounder on at this time, then do that and find other ways to connect with mentors and investors. If your business could benefit from the experience, social, and financial capital that a cofounder could bring to the table *and* that means also the opportunity to participate in an accelerator, then bravo, pull the trigger and get yourself a cofounder.
The accelerators I have pitched at want at least 2 co-founders to gain admission. Investors want the same- teams. Options to demonstrate your capabilities may be to plow ahead and build your prototype without a co-founder (ie: demonstrate that you can get the job done). And/or find someone who will act as an advisory "co-founder" as part of the decision process toward deciding if you want to create a legal partnership or not. This is a small step that shows the accelerator you can attract people to your venture. You will still need to show you can move forward on the prototype.
Having just hung out with the guy and talked about the experience at length, I'd suggest reading about Jon Crawford's experience with Y Combinator and how they treated him when he showed up as a single co-founder: http://joncrawford.com/post/20378314843/how-i-got-kicked-out-of-y-combinator-and-then-raised