Shut Down MySQL during InnoDB rollback after crash
No, rollbacks cannot be done in the background. Both that and the double write checks have to be done before accepting connections again (meaning that if you kill it, you will have to start again on restart). REDO process, however, can and is done in the background.

What you can do is kill mysql (again) and restart it skipping that step:

/etc/init.d/mysqld start --innodb_force_recovery = 3


Then drop the offending table and recover it from the backups, that may be faster than performing a huge rollback.

For the future, try to avoid huge changes on a single transaction precisely to avoid rollbacks, which can be several times more expensive that the actual commit. I can provide you with some tools to help you do this, if they are administrative changes. If the error was (by) a developer, I can only recommend you the option --i-am-a-dummy. :-)