The answer is highily dependent on what you are trying to achieve.
You could try using jquery to allow users to add/remove rows and then save all the entries to a single text field, using a delimiter of your choice.
When displaying the information to the user, you will need to read the text field again and use the delimiter to separate the value into different rows.
In summary:
- In the UI (javascript) you create and delete rows 
- You have a hidden input element for the text field that will actually hold the value 
- When the user clicks SAVE, javascript runs through the rows and 'collects' the values. It concatenates them to a string like VALUE1#;VALUE 2#;VALUE 3 and it save them to the hidden input field 
- The hidden input field is saved to the Sharepoint field.