Yes, you can use these ways on your flash drive to directly skip to Try Ubuntu or Install Ubuntu.
There are 3 ways:
The easy way: Download UNetBootin or PendriveLinux for Windows. Select your ISO, in this case, Ubuntu 12.04 LiveCD since you want it to boot directly to Ubuntu and not the menus. Select the Ubuntu ISO you downloaded, and the directory of your flash drive. If you want to prevent deletion of files every time you boot, check the "Enable Persistence" box. Just press Next and that's it! Your 12.04 Ubuntu will boot up directly to LiveCD.
The alternate easy way: If your bootable stick already has persistence (preventing deletion of files every time you boot), then open up Terminal (Ctrl+Alt+T) and type this command:
sudo apt-get purge ubiquity
This will remove Ubiquity, the LiveCD Installer. (Warning: You may not be able to Install Ubuntu using your USB after this.)
The not-so-easy way: Using YUMI or some other software, add a GRUB Bootloader to your USB stick and modify the boot menu to directly skip to LiveCD. I don't have any knowledge of this, you may want to consult other users.
But the first option is the best and does it's job without fuss. Happy exploring the world of Ubuntu :)