Service tax on delivery expenses

I am a delaer of excisable goods, and in the course of business undergo expense to the tune 12-15 lakh p,a on account of delivery expenses of goods to the customer.
Now all these expenses are paid to truck drivers/tempo drivers by cash but against vouchers and show them in my p&l a/c every yr.My queries are as follows:
 
* Had read that when a transaction (for a delaer of Excise) exceeds 750 (or 1500 in certain cases) the receiver of the service is liable to pay 2.575% (25% of 10.3%).. Does that mean i need to register in the service tax and start paying the taxes. I dont mind paying Rs 25000/30000.00 Service p.a , if paying the sum makes my expenses legal.
 
* These tempo/truck owners dont have any registrations /no income tax files, and will it be alrite if i pay without showing their names in the service tax...
 
* Most importantly, i have been incurring these expenses from 2007 onwards but came to know of this quideline only now... what should i do.. If i register now, would that mean that i will have to pay for all these yrs