I quickly had a mess around with this save last night. This is what I found;
True Adventurer & The Map Stones cannot be unlocked with this as they are already completed.
You can unlock some little trophies with this save such as;
... And away he goes, Precious!
Defeat Gollum as Gollum.
I've always been taller!
Use the Ent Draught on Pippin.
Return of the Mushroom King.
Equip Aragorn with the Mushroom Crown.
Worth greater than the Shire.
Dress a character completely in treasure items.
With this in mind I believe the following could be unlocked with this save;
A link to the elements.
Craft the Fire and Ice Bows. (Single Player Only)
The Last Mithril item is the Ice Bow
Don't tell the Elf...
Throw Gimli 30 times.
Can't test this as I got this legit
Our only wish to catch a fish!
Fish perfectly 20 times by pressing the icon as it flashes.
Dance of the dead.
Turn an enemy into a skeleton and make them dance.
An expected journey.
Travel to Trollshaws as Bilbo.
Taking the Hobbits to Isengard.
Travel to Isengard as every playable Hobbit.
We already know this
It won't be that easy!
During 'Prologue', jump into the fires of Mount Doom as Isildur.
If anyone could test this ones out, if not I will try to get around it later today.
Thanks Gandalf!