There's a very easy way to fill the gearbox oil
if you buy from Peugeot / Citroen it's Esso Gear Oil 75w80 with the PSA logos
here it costs about 15 Euro 2 liters.. not so much.
Use a funnel and a hose connected to it. put the hose in the filling hole and pass it to the top of the engine bay. so you can slowly add the oil by the funnel and it goes down with gravity.
That's how i filled my saxo few weeks ago and used to do in the S1 Rallye.
the other way is using one of these
that you can buy in most auto parts or tool stores...