Hi,
NI does not have any software that can do this.  I guess you would need to write a serial driver that uses the GPIB board (using NI-488.2 functions). 
The only quick solution I can think of is using the GPIB-232CV-A or GPIB-232CT-A external GPIB interfaces:
http://sine.ni.com/apps/we/nioc.vp?cid=10066〈=US
With this interfaces you could use one of the COM ports to communicate in a GPIB bus. 
Hope this helps. 
DiegoF.