it depends what you are wanting to use them for. if you want individually packaged seeds like masanobu fukuoka uses in his methods for planting rice and grains, the only easy method to use is to moisten the seeds, roll in dry clay powder, moisten again, roll in more dry clay, etc. if you are wanting to make seed balls that have a selection of different seeds in them for chucking into random patches of earth, as is used by many geurilla gardeners, then you'd just be able to get some wet clay, mix it in a bucket with some compost and some seeds, get it to the right consistency to roll into balls and you're away.