I haven't done this in a long time but I will see if I can remember how I use to do it.
You can add a double wire weed guard to a pre-tied Woolly Bugger. The problem is your head will end up being bulky. You have to tie in the wire and super glue it. With an existing head it can get large.
You can buy Metz Stainless Steel Weed Guards that work well. The are already bent into a loop that goes behind the hook eye. Here is how I would do it.
1. Slide the guard over the hook directly behind the hook eye.
2. Tie in the guard using a criss-cross underneath and over the hook and guard.
3. Add a drop of Superglue to the tie making sure you include the hook, thread and guard in the glue.
4. Once the glue is dry take needle nose pliers and bend the two weed gards back towards the hook point. Separate the two wires so they form a V over the hook point.
Normally the weed guard is bent into proper sharp before it is tied in but it may be harder to do with the fly already finish.
Here is an alternative way to bend the weed guard if you have flat jawed pliers. This works best when tying a new fly.
1. Grasp the weed guard at the loop about 1/16 to 1/8 of an inch down with the pliers. Make sure the bottom of the pliers jaw is at a right angle to the weed guard. Now make a 90 degree bend in the weed guard. What you will have is the weed guard with a small loop that lays over the top of the hook just behind the hook eye. The weed guard will be sticking back parallel with the hook shank. This gives you a better way to tie in the weed guard with the wires being parallel with the hook shank.
2. Tie in the weed guard and Superglue.
3. After the glue drys bend the weed guard down at an angle forming the V over the hook point. You should hold the weed guard with the pliers at the tie in point as you bend the wires down and back. This keeps you from breaking the glue joint.
This may give you some ideas of your own.
Metz Stainless Steel Weed Guards