Crude LM7809 9V NiMH charger
This isn't as straightforward as you are hoping.

At any given state of charge, the amount of current a battery will accept is function of the voltage you apply.  A current-limited battery charger basically varies the voltage so that the desired current is achieved.

You might be tempted to put in a big series resistor to limit the current.  The effect would be that of a voltage divider: the resistor will drop some of the voltage and the battery will drop the rest of it.  But this won't be controlled, and the voltage ratio (and therefore the current) will change over the charge cycle.

From Battery University (emphasis mine):


  It is difficult, if not impossible, to slow charge a NiMH battery. At a C rate of 0.1C to 0.3C, the voltage and temperature profiles do not exhibit defined characteristics to trigger full-charge detection, and the charger must depend on a timer. Harmful overcharge can occur when charging partially or fully charged batteries, even if the battery remains cold.