not helpful to you but I treasure my violets. They don't seem to smother other plants and while they are growing and filling space, I don't get less desirable things growing there. The colour in spring is a "freebie" as well.
If you do want to get rid of them, try a weed wand
http://www.argos.co.uk/static/Product/partNumber/7203525.htm
you will probably need to go over them more than once though. If there are things like dead leaves around then wet the area down first or wait till after rain as its easy to set teeny bonfires lol. You can stamp them out in suitable shoes or they burn out but its worth being careful in dry weather.