CLS, you must have a mono leader of at least 7m to absorb the shock properly, otherwise you will have the following problems.
1. You will pull the lure out the fishes mouth when he hits
2. If it is a biger fish the shock will part your line
3. If you line did not part as in 2 you will wear a big hook hole in his mouth and he will come loose.
4. You line will most likely part on any decent fish
5. If you fish goes for the bricks, you line will part
What I do is I make a wind on leader with a thin, light dacron and make a 40 turn bimini in my braid and connect with a 5 turn modified cats pawl.
For you 20lb braid you can make a 20-30lb leader 6.5m long and then add a 50lb shock tippet of 300mm if you need, for 30lb I would not add a shock tippet.
At the end of the line tie a small swivel and fit a forged spilt ring for attaching your lures.
The swivel will help with line twist and act as a short bite trace. With teh split ring changing lures etc. will be easy.