There is no difference in difficulty between a normal 1000 and LEL. Just a couple more days of riding, at a lower overall speed.
It's asking for the pass that concerns me, not the ride difficulty. I'm thinking of LEL as a normal 1000 with 200 flat km across the fens added in both directions and extra time. The mille penines is not a normal 1000 in my opinion.
When preparing for PBP,one of the ways that I fitted in a long ride (100 hilly miles) was to set off at 5 or 6 p.m on a Friday evening , with a plan to arrive home by 3 or 4 a.m. I could get just enough sleep to function normally on Saturday and do a ride with Mrs. M. on Sunday.
As others have commented above , you should aim to do an SR series to prepare for a long ride like LEL, but that is largely to build up endurance and experience how you react to long rides and night riding.
If you are a fast rider anyway, you may get enough sleep . Only you know your capabilities.
I decided not to ride PBP in 2007 due to family pressures, so know exactly the position that you are in.