In the same way you can work with multiple Picasa databases, it’s possible to link multiple SpiderOak accounts to the same PC.
Why? SpiderOak is good for backing up servers but using your home account for that is a bad idea. It’s better to set up a separate account so that if the server gets hacked, only its data is exposed.
In theory it’s enough to register the account, configure the server and forget about it – backups will be done automatically. But sometimes you have to administer SpiderOak, e.g. delete older versions of deleted files, which is easier from GUI. And switching accounts is a pain.
Create another Windows account and set up SpiderOak under it to use the server backup account. Now you can run SpiderOak from your main Windows account by Shift+right-clicking it and choosing "Run as…".