a couple of freely available tools, on
http://www.keyboard-layout-editor.com/ create a standard 60% layout then overlap your extra space position options on top of the existing spacebar like this,
["~\n`","!\n1","@\n2","#\n3","$\n4","%\n5","^\n6","&\n7","*\n8","(\n9",")\n0","_\n-","+\n=",{w:2},"Backspace"],
[{w:1.5},"Tab","Q","W","E","R","T","Y","U","I","O","P","{\n[","}\n]",{w:1.5},"|\n\\"],
[{w:1.75},"Caps Lock","A","S","D","F","G","H","J","K","L",":\n;","\"\n'",{w:2.25},"Enter"],
[{w:2.25},"Shift","Z","X","C","V","B","N","M","<\n,",">\n.","?\n/",{w:2.75},"Shift"],
[{w:1.25},"Ctrl",{w:1.25},"Win",{w:1.25},"Alt",{a:7,w:6.25},"",{x:-6.25,w:3.25},"",{x:-3.25,w:2.5},"",{w:1.25},"",{x:-0.5,w:3},"",{x:-2.5,f:2.5,w:2.5},"",{a:4,f:3,w:1.25},"Alt",{w:1.25},"Win",{w:1.25},"Menu",{w:1.25},"Ctrl"]
Now take your raw data and pop it into
http://builder.swillkb.com/ with options for pok3r 60% case and corners at 2 it comes out like this,
Show Image
From the builder you can order a custom plate directly from lasergist or download the files and get it cut somewhere more convenient for you. Would not try and do any cuts or modifications to a standard plate as you will probably just make a mess and end up binning it.