There's quite a bit of options available for peristaltic pumps with low flows. And small tubing is available from companies like Irama Corp - see this page for a list of small ID tubes that are designed for lab grade pumps. http://www.iramacorp.com/pump.tubes.htm

The smallest one, labelled "orange/black" can pump at 0.006 ml/min with a pump running at 0.5 rpm. That's pretty slow to me! Purple/White will get you up to 22 ml/min at 90 rpm - so there's a huge range of flow options available out there.

You're certainly right that there are issues with low backpressure and flow variability when using such small flow rates. But you can also get some pretty fine tubing for dispensing the liquid - much finer than regular syringe needles. My understanding is that 21 gauge is a commons size for drawing blood, and 30 gauge for insulin needles.

www.smallparts.com sells teflon (PTFE) tubing down to 44 ga. That's 0.002 inch diameter. I've got some from them that's 32 gauge. Even at small flow rates, that diamter will help smootly dispense the liquid being pumped.