This got me foxed for a short space of time first time I did it, not having a special tool.
You must always change the outer bearing surface for the spigot bearing (input gear transfer bearing) if you ever change this bearing as they are a matched set.
The way to do this, as well as to replace the idler gear too is to use a high speed grinder. I did it with a smallish grinding wheel in a dremel. Basically grind a slot forwards and backward at any specific point (easier if you do it at the bottom as you are using gravity) until the metal changes colour. This means you are about to break through. Get a screw driver and gently tap the ground line from the outer edge. The line should crack and the bearing will become loose and drop out.
Took me about 5 mins to so each one (idler gear bearing and input gear transfer bearing).
Putting the bearings back in is best using a press. Puts them back in square. I have one if you ever need one doing.
Cheers,
David