There isn't currently a way to effectively perk farm from the high numbered side. Being on the country with the highest population will actually reduce the perks you get per kill, switching near the end of a war "win" won't get you perk points either.
If you want to perk farm fly on the side that's outnumbered, combined with a high ENY plane (something in the 25-30) range and you can rack up 15-30 perk points per sortie.
Just to give you an idea of what this wish implies, if I wanted to switch sides you think I should pay over 22,000 perks points? Seems a little steep to me.