One is to sandwich the wire between two pieces of petals, which will give you a more opaque petal. The second is to use a small piece of wafer paper to cover the wire on the back of the petal.
The third is this: Get some gum glue, wires and petals.
Dip the wire in the gum glue
Stick the wire onto the back of the petal. The bumpy side of the paper is the back, since that will stick better than the smooth side.
Let the gum glue dry VERY well before you try to mess with the petal.
Remember to let the petal dry VERY well. The wire will come off if the gum glue isn't dried securely to the petal. Also, if you need to bend the wire be very careful since bending the petal can make it break or rip.
If the petal was colored before you put the glue on it the color will darken on the spot where the glue touches the petal.