I know that you can change the duty cycle of the 555 in that way, what I have is an oscillator already running with 50% duty and wanted a short output regardless of frequency. Styx suggestion has worked perfectly, I tried it earlier. I used a 2.2nF and 22k which gave around 0.5ms pulses after my schmitt (I have a scope now which makes everything so much easier).
I might as well show what I want to use this for. Its going to be part of my LFO project, which I want an S&H output included. I tried a couple of analogue circuits to no avail, but have came up with this which has some advantages aswell as some disadvantages (it can hold a value with no drift but is quantised)
The sim naturally didn't work, but i'll explain. The 6-bit counter is supposed to cycle through on one clock, giving 64 sequential voltage levels at the summing amp output when the D-types clock input is high. The clock inputs are controlled by my other oscillator, through the high pass filter circuit (this is so you can't hear it changing). So, when they are momentarily pulsed, they take on the D values and give a an output voltage. Because the two clocks are not linked, I would think the output values to be more or less random. I don't have the parts to test this, but is it likely to work. Possibly overcomplicated, but i'm not bothered by that.