(9) Manually set the default filter to not forward mail. Reverse to resume mail delivery.
(10) Options->Email Settings->Send Email To Handheld -- set it to No when you don't want email.
(11) If you have a PC on the same network as the BES install DM and check the "Disable message redirection while your device is connected" option under Email Settings (and connect the BB when you don't want mail delivered).
2 & 7 are my recommendations assuming that it is important for you to actually receive email the rest of the time. It's too easy to overlook re-enabling email delivery and I haven't seen an automatic solution aside from auto on/off which has its own set of caveats. Surely there's a place you can put the BB and ignore it? That's what I do on evenings and weekends (and vacation).
In any case, surely one of the 11 possible options will work for you.