Can you feel submissive without a dominant partner?
Not particularly. I envy those who can.
If so, how does your submission express itself? If not, how do you handle your submission or submissive feelings?
In the absence of D/s I turn to fantasy. This might be fiction, artwork, or simply what I create in my mind. I find ways to channel it. When successful, I find I can channel a mindstate that feel very similar to actual subspace. However, since much of my subspace is driven by feelings and emotions, this state requires a "focal point" of my feelings, which inevitably requires a character to fill the role of Domme.
While this is sort of a fix, it isn't super sustainable in the long run. Eventually I will inevitably ache to feel it for real. In these times I simply try to distract myself by immersing in a book, TV series, or the like.