I have an attachment which has a slide bar which you set for whatever seam allowance you want. It has been so long since I bought it it is hard to remember just where I got it.
I can take a picture and email it if you like. There is an online store that sells all sorts of extras for quilting and sewing machines. I really believe I got it there.
If you are interested in seeing a picture of this little thing, just pm me and I will be glad to take a picture and send. I have one for both sewing machines.
Mariah