heya, i found the answer to this problem.
a tool called directorybind. it's a little fiddly and requires basic knowledge about folders and files but it works..... PERFECTLY.
if you've ever used the linux mount -bind command, you'll know exactly what this is ;)
for others, basically this lets us remount part of a file hierarchy somewhere else (even another system)
a couple of things however
1. you need root access
2. need to be comfortable with file/folder structure.
after all, you have to know where the app + data is being stored in the phone and be comfortable moving it to the external sd card without accidentlaly deleting half your system.
on the s3 i did make 3 changes to the settings.
1. make sure to tick Alternate dbase mgmt, the reason i had to do this was because otherwise the binds i added would not save upon reboot.
this ensures my binds are automatically loaded every reboot.
2. default data path is "/mnt/extSdCard/Android/data"
3. default target path is "/sdcard/Android/data"
the last two settings makes it quicker to move apps
on my external sd card, i have the folders /Android/data created
now to actually add items to this.
lets take for example, max payne... this game is huge for a mobile game and chances are, we want it on the larger sd card.
in order to add this i would do the following.
1. press menu and select add new entry
2. press and hold the (target) path text box
3. you should see the max payne game directory (in my case this was com.rockstar.maxpayne) so now open this folder and press the select button
4. press and hold the (data) path text box
5. press the New button
6. type in "com.rockstar.maxpayne" without quotes and hit create (note you do not need to name this exactly the same as the target directory, but i do so it's easier to remember if i ever want to reverse changes.
7. press Select
8. tick Transfer files from target to data (this will move the files to the external card for you... it will keep the folder structure intact on the internal memory, but the files themselves will be moved)
9. press Add
this works perfectly for me, tested on mass effect, gta3, max payne, nova3, spotify
i suggest however that you avoid this unless you are comfortable to work with files/folders
i'll keep an eye out for any other apps that may be easier to use, but this is the best i've found so far.
oh one last thing, remember that in linux systems, folders and files are case sensitive, while i haven't checked this per-say on the s3, i assume this also true.
*edit* just realized you have to make sure the bottom right corner is lit green.
when you create a new bind, make sure it's ticked on the right side and tap the floppy disk on the left making it green.