This is easy for four resistors, just make two banks of 2 ohms and put them in parallel, bringing the total resistance back to 1 ohm.
+--+---+
| | |
| R R
V | |
| R R
| | |
+--+---+
In the above configuration, the middle of each bank (between the resistors) are equipotent with respect to each other. This means there is no voltage difference and that any resistor placed there will carry no current and not affect the resistance of the circuit.
Placing the fifth resistor here will satisfy the requirements of the problem.
+--+---+
| | |
| R R
| | |
V |-R-|
| | |
| R R
| | |
+--+---+
|
