No I don't think you can do that. the lower half of the seal is in the rear main cap. if you don't get that seal in there just right it pinches between the main cap and block. and then this summer you will be doing a motor job. you need to split the tractor and pull the flywheel rear plate and the oil pan. Or if the clutch is not getting oil soaked, Park it with a bucket under it and keep the oil full and run it.
Good luck Ed