Set STRSIZE and STRPAD of attributes

[lassemot]

I need to generate a H5 file which is read by some legacy system which requires STRSIZE and STRPAD to be set to correct values for attributes (it also needs to be ASCII). I'm doing something like this to set the attributes:
Hdf5.WriteAsciiStringAttributes(groupId, "To_area_id", new List<string> { "2" });

And I then get the following attribute (extracted using h5dump):

ATTRIBUTE "To_area_id" {
         DATATYPE  H5T_STRING { 
            STRSIZE H5T_VARIABLE;
            STRPAD H5T_STR_NULLTERM;
            CSET H5T_CSET_ASCII;
            CTYPE H5T_C_S1;
         }
         DATASPACE  SIMPLE { ( 1 ) / ( 1 ) }
      }

But I need to get:

         DATATYPE  H5T_STRING {
            STRSIZE 1;
            STRPAD H5T_STR_SPACEPAD;
            CSET H5T_CSET_ASCII;
            CTYPE H5T_C_S1;
         }
         DATASPACE  SIMPLE { ( 2 ) / ( 2 ) }
      }

Is this possible somehow?