Normally this is something, that Google needs to implement asap. It is totally annoying, that it is diffcult or sometimes impossible to transfer save games from one device to another.
I'm using a phone and a tablet - and it would be great if i could use the save game on both devices without any manual copy procedure - which is sometimes not possible (Not everybody wants to root his device).
I already thought about online savegames - to have an online slot. Only problem is, that I am not sure, if my current server structure is able to handle such amounts of data (additional running costs).
It would be very genious if google would offer online space right out of the box, but that's not true at the moment (would be very cool *g*)
But I can clearly see your problem and switching the sd card is not a perfect solution.
Also uploading the savegames (which can be quite big) to an online location would need a bit of time so I cannot do that regulary.
Will think about that - at least it opens doors to new online features of the game. If you have any further feedback or suggestions just let me know ;-)