This is the line of code used in Athena to run pucrunch:
pucrunch -d -c0 -r255 Athout_i.bin Athout_c.bin
Where the underscore characters are filled in with some character 0-9,A-Z
If you really want to know, this is the function I wrote to do the job. Some of the casts just aren't necessary, but still. I'm a newb when it comes to the C thing.

const char *alphanums = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const char *tiheader  = "**TI83F*\x1A\x0A\0Built using the Athena Packager Software  "; //53 bytes
const char *tifileheader = "**TI83F*\x1A\x0A\0";
const char *athenaheader = "\xBB\x6D\xC9\x31\x80\x00\x01\x09";
int flushtofile(char *inputstream,int appendfilenum,int outfilelength)
{
    char tempfilename[]="Athout_i.bin\0";
    tempfilename[6] = alphanums[appendfilenum];
    FILE *newfileptr;
    newfileptr = fopen(tempfilename,"wb");
    if (newfileptr == NULL) return 1;
    if (outfilelength!=fwrite(inputstream,1,outfilelength,newfileptr)) {
        printf("Err: Could not flush buffer to file!");
        (void) fclose(newfileptr);
        return 1;
    }
    (void) fclose(newfileptr);
    if (!system(NULL)) return 1;
    char tempbatch[]="pucrunch -d -c0 -r255 Athout_i.bin Athout_c.bin\0";
    tempbatch[28]= alphanums[appendfilenum];
    tempbatch[41]= alphanums[appendfilenum];
    system(tempbatch);      //pucrunch will always output some sort of error. Newp.
    remove(tempfilename);  //assumes it can be removed. We just created and closed it...
    return 0;
}