In token contracts where tokens can only be held by permissioned owners, this allows for a backing token. Trades at the price of the real token - risk of having account seized for bad behavior :~)

AndSomeNonMembers.sol

pragma solidity ^0.4.15;

import "./MembersOnly.sol";

contract AndSomeNonMembers {
    MembersOnly token;
    mapping (address => uint256) balances;
    mapping (address => mapping (address => uint256)) allowed;
    
    function AndSomeNonMembers(address _tokenAdd) {
        token = MembersOnly(_tokenAdd);
        balances[msg.sender] = token.balanceOf(msg.sender);
    }
    
    function transfer(address _to, uint256 _value) returns (bool success) {
        require(balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]);
        balances[msg.sender] -= _value;
        balances[_to] += _value;
        return true;
    }
    
    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
        require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value > balances[_to]);
        balances[_to] += _value;
        balances[_from] -= _value;
        allowed[_from][msg.sender] -= _value;
        return true;
    }
    
    function balanceOf(address _owner) constant returns (uint256 balance) {
        return balances[_owner];
    }
    
    function approve(address _spender, uint256 _value) returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        return true;
    }
    
    function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }
    
    // Finalizes transfer in the actual members only contract
    
    function finalizeTransfer(address _to, uint _value) constant returns (bool success) {
        require(balances[msg.sender] >= _value);
        balances[msg.sender] -= _value;
        if (token.transfer(_to, _value)) {
            return true;
        } else {
            throw;
        }
    }
}