pppd and wvdial are 2 very different animals. I'll try for wvdial only
10 years since I did much with it, but I think it does take a -c /path/to/config_file option, and you can set that as 0600 owned by root:root. You might use this
alias wvdial="wvdial & exit"
I could open up a root terminal, tyoe 'wvdial & exit' and the terminal would vanish back to a login screen, you'd lose the gibberish it throws out but you could hear the modem doing it's thing. I had a huge respect for the hacking power of my kids.