Magento admin for substores

We have a magento admin through which we manage several websites but it seems with the free edition of magento we cannot create admins for each of these websites. We are looking for some solution through which we can create a separate admin for each of these websites managed through our magento admin. Along with your bid please let us know what you will do to achieve this and also examples of the link incase you have done this for magento websites in the past.