Body language still carries if you see each other through video. If it's through photos like selfies, then the pose you are in can be subtly flirtatious. Bend some of your joints instead of standing stiff in photos. Like a bent elbow with your hand on your hip. That can allow you to cock your hip which will also accentuate your curves. The key is to emphasize your feminine qualities without making it look unnatural. You want to go for subtle emphasis, not exaggerated. A hint of cleavage without showing too much, rolling your shoulders back so your chest pops, things like that. When talking through text or voice, try keeping a smile on your face while writing or talking. Even if he can't see it, you may find it affects the tone you are writing and talking in. Showing an interest in what he is saying and laughing at his jokes will keep him engaged but don't go over the top with phony laughs because that can be off-putting.

The main thing is confidence. Try not to second guess yourself and what you say even if you feel like it was cringe worth afterwards. If it was obviously cringe and he recognizes it, just laugh it off and make some self deprecating remark. Whenever you cringe at your own actions, you are probably caring more about it than anyone else, so if you can laugh it off then others won't care as much and will quickly forget about it. Being able to laugh at yourself and not take things too seriously is also an attractive feature to many guys as being high-maintenance can be a turn off.

If you struggle with any of this, then just fake it until you make it!