Hi Ditto, there are a couple of plug-ins that you can add in to get some construction lines that last for longer than the current command, check them out here:
http://kyticka.webzdarma.cz/3d/moi/#KeepCLine

If you set up the script there labeled "Keep construction line", on a shortcut key, that will then cause any construction lines created inside of the current command to stick around after the command is ended instead of going away automatically like they normally do.

Also see here for a custom command that you can set up that is just for setting up clines that stick around:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1029.1


It would be nice in the future to add in some more methods for manipulating construction lines, but it can be hard to figure out a good UI for managing them that is not too obtrusive.

- Michael