Not sure if this is what you are asking. Aplogies if its not
Select Rwy and and suitable Rwy extension (say 3.1Nm) and 3 degree path.
Execute.
Join the dots.
Then Input a new point inside the Rwy ext (say Rwy Ext/ - 0.1)
New point is created.
Execute
Now you can delete/overwrite the original Rwy ext (it has done its job).
The new point at 3.0 nm is now a lot more friendler and can be used to build a base leg off.
Full circuits can be 'built' but its a lot more fun to **** it up yourself.