This was actually just what the Russians did in the Brusilov offensive in 1916, where they dug hidden trenches towards the Austro-Hungarian trenches to insure that the soldiers did not have to cross a wide no mans land.

I'm not sure, but maybe one of the reasons why this succeeded was that there was no vigorous patrolling of no mans land by the Austro-Hungarian army. If you detect such trenches, you are warned that an attack is imminent and you can direct artillery towards it.