I think it's pretty common for a 1/4" foot to also have a mark for 1/8" seams as well. When the needle is in the center position (0), the distance to the end of the foot should be 1/4". So if you line up your fabric with the edge of the foot, is the distance from the stitch line 1/4"?
Then is there a halfway mark on the foot between the needle and the edge? That's the 1/8" mark.
Once you know your marks you can play around a bit with a scant 1/4" to get your measurements more exact. You just have to do some stitch and measure with a very precise ruler.
Hope that helps, post pics or explain more for additional help please :-)