Script update. Fixed few bugs. Changed internal structure. Script modifications should be easier.

Frenchy Pilou
>> Must I draw them separately ?
Yes, you should draw them manually.

>>And alas we can't use the Helpers lines for align because of the second click ! :)
You can use LockConstructionLine script

var cln =0, gd = moi.geometryDatabase, cl = gd.getObjects().getConstructionLines(), cll = cl.length; 
for (var i=0; i<cll; i++) if (!cl.item(i).isTemporary) cln++; if (cln == cll) { gd.removeObjects(cl) } else { cl.setProperty( "isTemporary", false ) }

Bind it to key. Draw construction lines. Run script (the lines will be locked). Run script again to delete the lines.

Hamish, Chri, phlatt5th
Thank you :)