Add '{' and '}' to the RE_ESC rule in boo.g and booel.g to allow the use of curly braces in regex literals like so:
s = """stuff { { code } } omg { more } pwn"""
mc = /(?<Unable to render embedded object: File (\\){(\\\{) not found.\\){.*(?<Unable to render embedded object: File (\\)})*(?<) not found.
)}/.Matches(s)
for i in range(mc.Count):
print mc[i].Value
mc = @/(?<Unable to render embedded object: File (\\){(\\{|\\}) not found.\\){.*(?<!\\)})*(?<!
)}/.Matches(s)
but if you do make these little additions to boo.g and booel.g, both forms work (escape and non-escaped curly braces)