You can add an empty "work" PBL at the top of your library path and copy the object you want to "check out" into that PBL.
If you are online again and have a network connection, check out the object in the original PBL and copy/move the object back from your "work" PBL.
Also in the Source Control options, you have an option "This project required that I sometimes work offline".
hth
Arnd