Our situations are somewhat comparable, it seems. I would be glad to lend my strength to the Force [Sebastian's kingdom for something semi-productive to do. waiting on Ciel and his aunt only take up so much of his resources] but that would happen on my master's orders.
Should joining it demand of me to neglect my master even a little, however... [his smile turns slightly loop-sided as he lightly shakes his head: in that case, they'll have to do without him.]