I don't have any of the bleed kit handy so it'll have to wait but I was thinking of using a smaller spacer block and then adding more fluid with the method linked above.
I'm pretty sure it'll be fine with whatever is in the reservoir, at least until the pads wear down as there will be enough to compensate for that anyway. I'd just try what I said and avoid putting the bike upside-down.
I don't have any of the bleed kit handy so it'll have to wait but I was thinking of using a smaller spacer block and then adding more fluid with the method linked above.