Fred,
Just a comment, looking at the problem from a different perspective perhaps.
Do you need to constrain everything in the sketch? Depending on what you are engraving you may not benefit greatly from constraining everything if you're unlikely to want to change it for any reason. NX works just fine in most cases without having to have each and every sketch fully constrained.
If it is a repetitive patter of some sort you may want to sketch the first instance of the pattern and then build the model with an array to produce several identical copies.
Hoping this helps
Regards
Hudson