Next time you smell it, lift up the rear driver side seat base, you'll find a black plastic cover in the floor. The fuel pump is directly under that cover. Take off that cover, leave the seat up and drive again.
If the smell is worse then it could be a little seepage past the seal on the fuel pump or could be a little seepage on the o-ring inside the two clip on fuel pipes.
I wouldn't recommend a DIY fix on the fuel pump as it is mandatory on peugeot's to replace the pump seal every time the pump is taken out. Also without the correct tool it is very hard to tighten the black ring again to the correct position without snapping off the lugs and breaking the ring.
Sean, October 2009