A while back we took at look at a tool called BarInstall that allows you to install BAR files (aka sideload apps) to your BlackBerry 10 device without the use of a Mac or PC. The app requires a premium account at which point you can upload a BAR or APK file and easily sideload to your device OTA.
A new version has been released that is sporting Localbar mode - essentially a free way to install BAR files to your device from your SD card, albeit with a bit of work. You'll need to setup a proxy using a computer, Android device or even an old BlackBerry, but then you can install any BAR files from your SD card without the direct use of a computer.
It does take a bit of work to get it all setup, but if being able to sideload on the fly is important to you, it may be worth checking out. The developer has started a thread in the forums with all the goods so if you're having trouble getting going, be sure to swing by and get yourself sorted out. You can download the localbar app here and check out this page for more help with both the free and premium version.