How to make the labourers get at-lest the gross minimum wages to their hands ?

I am working in a government organisation. We call tenders for engaging labourers (skilled, semi-skilled and unskilled) through 'contract agencies'. Here our people are following certain procedure which, I feel, gives loss to the working labourers finally. The tenderer/contractor has to quote more than 18.36% (12% EPF + 4.75% ESI + 0.5% EDLT + 1.11% Administrative Charges) of the 'minimum wages' set by the state. Whoever quotes less, he is the L-1 and he will be awarded the contract.
Ex : minimum wage for skilled-labourer in Bangalore : Rs.2545.00(Basic)+Rs.933.00(VDA)=Rs.3478.00(Total) .
Additional 18.36% = 3478 x 18.36% = Rs. 638.56
That means total = 3478 + 638.56 = Rs. 4116.56
So, the contractor who quotes more than Rs.4116.56 but who quotes the least among all participants is the L-1. For example, a contractor, in fearing of losing the contract, may quote exactly Rs.4116.56. Then he will be the L-1 contractor.
But the problem is how can he get his profit. So he is paying only Rs.3000/- only to the labourers, where as the minimum wages is Rs. Rs.3478/-. That way the poor labourers are losing their minimum salary also. I heard the contractor is showing to EPF department that he is paying Rs.2100/- only as Basic+VDA to the labourers. That way the labourers are losing their EPF contribution also.
So, please clarify me regarding the following please....
1. Whether, legally, is it possible that our office tender itself should say that the contractor has to quote a "minimum amount", say Rs.5000 in the above example ? Can we justify to the vigilance department ? I mean, does any organization, legally, has the authority/discretion to decide a 'minimum amount limit' more than the minimum wages decided by the government for the labourers which the organisation is going to engage through 'tender' ?
2. Is it possible that we insist the contractor to pay the gross minimum wages to the labourer as the net pay after all EPF and other deductions ? Is there any ruling that employee's contribution part of the EPF should be deducted from the gross minimum wages put by the government ? I mean, in the above example, whether the EPF of 12% of Rs.3478/- which is Rs.417/- should be deducted from the Rs.3478/- only ? But then the labourer will get even less money to his hand, right ?
3. Straight one question ? Is there any way to help the labourers so that they will get atleast the gross minimum wages, Rs.3478/- in the example, to their hands, even after deducting all the EPF and other deductions ?