Feeding brakes through frame help..

I need to fit new brakes to Sonder Evol I have, after the PSA for Dominions on here, i missed out on that bargain, but brought some of the cheap 4 pot Shimano Deore.

Being CRC they have come with levers wrong way round, so LH front etc, so need to swap over levers anyway.

But at the lever end the hose enters through a small hole into frame, but exits at a decent "hatch" by the BB.

So If they lever is off, i would be trying to thread the hose from the BB end with calliper on upwards? As opposed to the easier down the frame, as i don't want to lose brake fluid and the brakes levers are off anyway?

Does that make sense, or am I best to just swap levers over, and remove calliper to feed from top potentially losing the fluid in the lines... ?