Extending the fuselage towards the nose is a good idea but don't get excessive. Extending it another 20% should suffice, 50% is probably too much. How do you extend it?' Review the following process-
1) Find wood of the same size as used on the fuselage originally.
2) Position the new extension piece under the nose.
3) Cut a long angle cut through the fuselage and then indent the extension piece underneath.
4) Cut the extension on that same angle.
5) Check that the extension mates to the original fuselage with a flush joint.
6) Use a little five minute epoxy at the top and bottom of this new spliced joint with a little super glue medium viscosity in the center. Join the pieces and accelerate the joint (use an assistant?).
7) Once the joint is cured, wrap the new spliced joint with thread and glue.
8) Add new launch tooth assembly to the nose.
9) Add a layer of 1/32 balsa sheet, cross grain, to the new nose assembly as a lamination.
10) Use CA glue and glue a bead of clue to the very front of the nose. Let cure.
11) Check the center of gravity picking a point about 1/3 back from the leading edge of the wing. Check the balance.
Chances are that the nose may become heavy enough to be nose heavy and the glider dives. To counter this before you catapult launch, pinch the trailing edges of the stabilizer (sanded to at at least 1/32 or less!) and bend in a couple of degrees of "up" elevator. This will help the glider recover from a dive and also help in the transition. BTW, glue a smear of clay to the bottom of your launch handle so that you can can or remove clay from the glider as you trim fly.
If the glider stalls now, add a little more clay to the nose. The amount of clay may be deceivingly small to have a glider flying "like its on rails".