How to keep cake topper from toppling over

You can make the base wider with white chocolate. No glue, and you can do it in advance so you don't need to have any electricity at the site.

Put a parchment paper round into an appropriately sized cake pan or a plate or shallow bowl. Stand the cake topper in the middle of the parchment paper. Carefully pour or pipe melted chocolate around the edge of the base and build it up, coating the base and widening it. Allow the chocolate to cool, carefully peel away the parchment paper.

If the weather is likely to be warm, you may want to make the additional chocolate layer thicker so that it will not melt quickly and release the topper.

You could also widen the base with some other material (cardboard covered with foil, for example -- make a large cardboard disc, cut a hole in the middle for the stem of the topper, cut a slit on one side of the hole the size of the base, slide the base through and center it) and cover that with chocolate or frosting, but I think plain white chocolate would work well and it sounds like the bride wants to keep everything touching the cake edible (except the topper itself, of course).

There are lots of other ways to attach a topper to a dowel that don't involve glue. (eg, screws)

Here are some other alternatives:

• fix the topper to a wider base, so that you can just set that on the cake. Something like plasticard (thin, white, can be drilled & screwed from underneath (use stainless steel pan-head screws; might want to wash them first to make sure there's no cutting fluid on anything else on them)). You can then cover the new base in flowers, fruit, fondant, or icing (either to match, or to make 'moss')

• Insert dowels (or stiff straws, or similar) into the cake to support the topper, all the way to the base of the cake, and then trim them flush with the cake. Set the topper on the dowels. If you're using slick plastic, you might be able to lift the dowels back up an 1/8" after finding the bottom plate before trimming flush, so that the topper can sink just slightly into the cake. (mark the dowels when all the way down so you have a reference mark, then spin them as you lift up to minimize friction ... you might want to set a central dowel just to test if this is going to be problem with your cake or not, so you know the topper will cover it if something goes wrong).

update:

• Make a wider base from plasticard, but afix it with something non-damaging that you can let set up before you get there. (eg, frosting as a mastic, or hot glue)

• Attach a dowel to a wider base (eg, a counter-sunk screw that just barely catches a fender washer ... you'll want a larger dowel, and pre-drill it so it doesn't split), then use frosting or hot glue to affix the topper to it. As another alternative that doesn't require as wide of a dowel, find an appropriately sized T-nut that the dowel fits tightly in (the threads should compress the dowel some). The dowel should be shorter than the height of the cake (as we're not going to be able to trim it once it's inserted).

I would suggest a miniature "tree stump" made of sugar; will match the theme and hold well if you stick the topper in the sugar.

Something like : http://www.foodmigration.com/2005/11/pulling-sugar-burning-thumbs.html