First, a subG class 2 isn't a great candidate for composite. 1mm isn't too bad, but by the time you get subG, there isn't much cervical enamel left (if any) for good bonding, and you'll end up with leakage and recurrent caries. Even if there is a tiny sliver of enamel left, isolation is really difficult. You probably won't be able to use a rubber dam. I would pack 00 or 000 retraction cord soaked in hemodent, apply hemostat to the papilla, and jam a tofflemire or greater curve band down there on top of the cord. You may need to use an electrosurge/radiosurge unit to reduce that interproximal tissue.
If you're dead set on composite, apply chlorhexidine to the dentin and selectively etch the enamel before restoring.