Clan micromanagement does not include this behavior. This is another design decision. I think it makes sense but this should be decided by top first. I can suggest it if they accept it can be added.
However in that case will not player always call them and move at map all together. What will stop him to do this? Actually still this is case if you are vassal. Maybe having reduced speed when army is formed is preventing player to all time moving together (because there is no influence cost for clan parties). However here you want something not in army form. So you also do not want speed penalty if I understand right. But in this case player always do this. Probably if they (also I) accept adding "forming army even you are not part of any kingdom". I do not think other solutions can be accepted. You should get speed penalty if you are moving 500 men.