Transfer the level 48 shaman to the main account. Level the character solo.

Make sure to use +10% XP shoulders (40 emblems of heroism or 200 stone keeper shards) and the new patch 3.2 +10% XP chest (40 emblems of heroism or 60 champion seals) for a total of 20% bonus XP. This is applied after rested XP, so you will get 240% rested with both items equipped compared to 100% xp non-rested without the items.

Also note that you will be able to level faster with the mount changes. Epic ground mount now, flying in outlands from 60-68, flying in northrend from 68-80.