Interesting, this constant current source notion.

For a design without feedback, and in an energetically inefficient way, maybe this can work too:

1. Determine what will be the maximum resistance of the "current consumer" part of your circuit throughout its operation.

2. Prepare a resistor several magnitudes larger than the resistance above.

3. Connect to the resistor above a (huge) voltage source so that the resulting current is the one you target for your current source

4. Put the "current consumer" part of your circuit in series with the large resistor.