It is possible to bypass DRC errors for debug purposes. Both the logical and physical DRC checks can be disabled with environment variables. Logical DRC errors contain the string "LIT", whereas Physical DRC errors contain the string "PhysDesignRules".
To disable Logical DRC checks:
Windows
SET XIL_MAP_SKIP_LOGICAL_DRC=1
Linux
setenv XIL_MAP_SKIP_LOGICAL_DRC 1
To disable Physical DRC checks:
Windows
SET XIL_MAP_NODRC=1
Linux
setenv XIL_MAP_NODRC 1
For more information on DRC checks, see (Xilinx Answer 35505).
For general information about setting ISE environment variables, see (Xilinx Answer 11630).