making the wordpress/blog location relative

it is extremely annoying that the location of the wordpress and the blog have both to be absolute. eg https://123.456.789.1/wordpress or such. I have a setup, where my working environment is having the server and a notebook on a router then comes the LAN. Either I enter the adress from the LAN side, eg https://123.456.789.1/wordpress or I enter the IP of the server from my island eg https://192.168.1.5/wordpress. This means the blog eventually is only visible from one side, but not from both. I tried everything imaginable to have a relative path eg ./wordpress but failed.