I suppose you could put a dollop of Silicon on the copper pipe, then push it into the bottle base, and wait for it to set-up. Then mount the flower on the rebar. Just a guess

Here are a few suggestions that may help you.

1. use shims (small pieces of wood) at least two (one on each side, four would be better) to steady the totem.

2. Since you are using wine and beer bottle, get corks (hobby stores and poss. wal-mart) drill a hole in middle just big enough for re-bar (You want it very snug) and trim cork to fit into neck of Beer/wine bottle.

3. You can get wood dowels large enough to snuggly fit into the Beer/wine bottles. Trim the end of the dowel to a point so it will be earier to pound into the ground.

4. make a wood cap for the rebar (don't drill all the way thru) glue the cap to the rebar (I use E6000) or make a cap out of a cork and then put a good dab of glue on top of the cap,let the glue set up a few minutes before put the totem on.

Hope this help. Chelcass

You can buy a foam covering to put on pipe to insulate them, the foam tube is slit to easily go on the pipe, cut a small piece, couple inches long, slip on the rebar or pipe you are using, you can put a bit of silicone to hold it on, then slide the bottle on over the foam it will hold it in place.
You can also use Styrofoam peanuts pushed in to take up the slack in the bottle neck.

Don't stress about them being crooked. Gives them character to tilt!!

I have heard people say they use a plate as a base for their totems, which they bury in the ground a bit, or cover with mulch, rather than using the bottle on rebar.

Yes that's what I do. Use a heavy plate or the old heavy ash trays work or anything flat and weighty. Keeps your totems straight. Even some old farm implements such as a disk or one I made using a glass block as a base. Good luck!