Now you're talking complex! A compressor bleed air system will require a pressure regulator, overpressure safety valve, and most likely a heat exchanger to function properly. Not to mention the significant power loss created!
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Lt Dan,
Well it has already been done. I talked to the boys fromJetworld in Germany when the visisted the JMA AGM in the UK a couple of years ago, and they showed me a prototype system. They then published details in the German Jetpower magazine.
A pressure regulation system would be required but a simple mechanical device could be used. Getting one small a light enough might be the problem. Pressure loss has already been dealt with, it's insignificant; but the point you make about temparature rise may provide a difficulty. When you compress air it gets hot, but is air bled from our compressors hot enough to cause a problem?
The lack of a commercailly available system has prevented me from going any further with this idea.
Regards,

John.