I was unclear in my comment. It is the ratio of hole size to pad size that seemed odd..The annular ring is calculated from that. Here's a recent example of a slotted and plated mount:
The pad diameter is 1.42 mm, drill is 0.6 mm, and slot is 0.6 mm x 1.6 mm. Oshpark has no problem with the board. If you make your pad proportionately smaller, then the soldermask will take care of itself. You can also define a smaller soldermask setback, which should not be a problem with such "large" components.
I don't think you will have a problem with shorting. In my experience, soldering over a gap is hard to do, unless it is very small. Please keep us updated.