towgs snd prj files

This might be a bit off-topic.
I do:

wpBert700 at proj4string

CRS arguments:
 +init=epsg:23031 +proj=utm +zone=31 +ellps=intl
+towgs84=-87,-98,-121,0,0,0,0 +units=m +no_defs

writeOGR(wpBert700,dsn="wpBert700v2",layer="wpBert700v2",driver="ESRI Shapefile",overwrite=T)

But the created prj file:
PROJCS["UTM_Zone_31_Northern_Hemisphere",GEOGCS["GCS_International
1909 (Hayford)",DATUM["D_unknown",SPHEROID["intl",6378388,297]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",3],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["Meter",1]]

lacks the +towgs84=-87,-98,-121,0,0,0,0 information, which is a
problem if I do not remember I have to add it for a GIS display
with reprojection on the fly.
Is there any vector format that can  be written by rgdal in which the
CRS info would include the +towgs84=-87,-98,-121,0,0,0,0 ?

Thanks!

Agus