Sending 4 empty bits

As @allObjects says, it's not possible to send just 4 bits via I2C on any platform, it's just the way I2C works - you have to send a byte at a time.

Your best bet is to send a whole byte and only use the bottom 4 bits - so sending 0b0000 like you're doing with Espruino is fine.

but reading the empty byte and printing it out seems to take a lot of effort in C++

Welcome to embedded software! :)