Yes, you can do this (although I haven't done it personally, so this is partial speculation).
You will need the SDE command line tools installed somewhere, either on your server or on a machine that can reach it over the network. The command you will need first is sdesetup:
sdesetup -o install -d SQLSERVER
[-H <sde_directory>] [-u <ArcSDE_admin_user>] [-p <ArcSDE_admin_password>]
[-D <database_name>] [-s <datasource>]
[-l <key>] [-N] [-q]
You can then connect to your SDE repository using Direct Connect (rather than the SDE service on port 5151). Note that you will still need a valid ArcSDE product key in your database.
There may also be issues with ArcSDE and SQL Server 2008 R2? I'm not sure on those, so perhaps someone else has some input.