Thanks guys.
I've decided I'll go with the series capacitor option to reduce the number of components and limit complexity.
I've calculated (and checked with the scope) that the inductor only takes 200uS to saturate, so even at the fastest frequency I think I'll ever need its much faster than required.
I'm already using an inverter gate/schmitt trigger elsewhere, so if I can use another one of them the same that would mean I don't need any new types of components.
I've come up with a proposed circuit (see picture). I decided I need to add a series resistor before the capacitor to limit the current in/out of the microcontroller (which is supplying the square wave). I decided on 470R as I'm already using one elsewhere and it seemed like an appropriate value (approx 10mA current at 5v).
I have found the switching threshold voltages for positive/negative going transitions in the Schmitt trigger/inverter gate datasheet. Obviously there will be a bit of pulse length variation depending on how the schmitt trigger performs (temperature etc.), but working with the min/max values specified I'm sure I can find something that works (it doesn't matter if its on too long as I have plenty of time to work with).
I'm at a bit of a loss on how to calculate the capacitor and resistor values connected the inverter gate input, so as to create the desired pulse length. I'm familiar with calculating the RC time constant, but the additional 470 ohm current limiting resistor on the other side of the capacitor confuses me. How do you calculate the time constant when you have resistors on both sides of the capacitor? I'll probably just try a heap of different values until I find something that works, but it would be nice to know how to calculate it as well.
Cheers