Dear Gargi: As pointed out by LLI, by mutual agreement such legal liabilities cannot be overcome. However, the following provisions of the ESI Act could be considered, if you are genuinely interested to be exempted from the Act.
87. Exemption of a factory or establishment or class of factories or establishments
The appropriate government may, by notification in the Official Gazette and subject to such conditions as may be specified in the notification, exempt any factory or establishment or class of factories or establishments in any specified area from the operation of this Act for a period not exceeding one year and may from time to time by like notification renew any such exemption for periods not exceeding one year at a time.
88. Exemption of persons or class of persons
The appropriate government may, by notification in the Official Gazette and subject to such conditions as it may deem fit to impose, exempt any person or class of persons employed in any factory or establishment, or class of factories or establishments to which this Act applies from the operation of the Act.
91. Exemption from one or more provisions of the Act
The appropriate government may, with the consent of the Corporation, by notification in the Official Gazette, exempt any employees or class of employees in any factory or establishment or class of factories or establishments from one or more of the provisions relating to the benefits provided under this Act.
But in all these cases you have to establish that your establishment is providing benefits at par or better than that is provided under the Act from time to time. It is a herculean task particularly looking to the medical benefits to the whole family, sick leave payment etc.