There is no option of not covering them.
For all those not covered, both for locations outside ESIC coverage and those with wages above ₹15000, you are open to risk of compensation for any accident. So for those employees you need to take the workman insurance cover. Remember that any other insurance like group cover, accident cover, etc is not going to cover compensation under employee compensation act. Courts have already given judgements clarifying that any other cover like accident insurance is additional benefit to the employees and the compensation under WC is still applicable. Only workman compensation act insurance cover which specifically reimburses the compensation under the act will be adequate.
Incidentally, ensure you are paying cess under BWOC act also
Actually, ESIC only comes to social security of all the employees and its replacement of WC policy.
1. Whether the site is in ESI implemented area? If yes employees drawing gross up to Rs. 15000 pm need to be covered under ESI & if there are site employees drawing more than Rs. 15000 pm they need to be covered under Employee Compensation Act policy.
2. If the site is in non-implemented area all the site employees should be covered under the policy.
Either the employees should be covered under ESI & or under the policy.