One problem when bending a Venetian cutaway is taking the side off the bender.  The metal slat on the bottom wants to spring back and can crack the tight bend.  This has worked well for me.  Get a length of thin ribbon that is made of non-stretchable material and use it to hold down the lower slat.  Just position it when you make the sandwich where the cutaway will be.  Tie it down after the bend is made.  If it is thin enough it won’t affect the bending process.