As trublu stated, you should really wait until the forms are set before you place the wells. If the well is rated for use IN concrete at all, the manufacturer should provide some helpful tips for the particular model you are using.
As for securing the fixture for the pour, I've strapped them to the rebar as tight as possible, and, if the concrete guys don't mind, you can also pour a sonotube around the fixture and at least one of the nearby rebar rods for stability. Leave the top of your footer at least an inch or two below final concrete grade so as not to disturb final concrete finish. Most concrete guys I've worked with are pretty cool, and most will have no problem with this as long as you let them know ahead of time.
Good Luck!
