It's not impossible - my employer has paid for my fees throughout my PhD, albeit part-time. You'd have to put together a good proposal that shows how they would benefit from you doing the PhD you've got in mind, as I doubt pure altruism would be a motive for them to sponsor you. Think about what they'd get out of it and why they should sponsor you - would it enhance the way you do your current job, or would it open up future potential business prospects for them? How will it impact on the time you spend in your present job - they won't want to lose out, either with your ability to do your current job, or too much financially. Can you negotiate a drop in days that you work maybe, to allow you to study? Or will it be so potentially useful to them to sponsor you that they would fund you full-time to do the PhD? Also, it's a long haul doing a PhD, so can you demonstrate in concrete terms that you've got the determination to see it through and not waste their money?
Why don't you think about it from their point of view, the pros and cons for them as a business, and maybe mention it to your manager or someone else appropriate, maybe in human resources, to sound them out? It probably sounds a bit cynical, but in asking for funding from an employer, the bottom line is always what's in it for them, particularly in the current economic climate. It's definitely worth exploring though, if that's what you want to do.