I couldn't find a way to put it at the beginning
Using regex
[Xx][Ii][Aa][Nn][Oo]
Using regex
[Xx][Ii][Aa][Nn][Oo]
How about:
^1[Xx][Ii][Aa][Nn][Oo]
Sadly the program appears to ignore ^
I had tried:
^[Xx][Ii][Aa][Nn][Oo]
and I've just tried your suggestion (shortened to ^1[Xx][Ii])
and it output:
1LztLGfb5dWntB1XinGyET94coN4Zds3Fx
Indeed ^1[Xx][Ii] doesn't do what you want in vanitygen. I once found a way to look for regexes at the beginning of an address (after much experimenting and delving into the source code) but I can't remember what the trick was for the hell of me...
I may take another look at it if you're really interested.