I don't think you can, but if you need a momentary boost you may think of a rechargeable battery and couple of transistors to your circuit.
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Also let's hope that you didn't write your question properly and saying that your embedded system IO pins gives 500mA and you want 1.5A.
In this case you use this 500mA as a signal to a transistor's Bios, and let the transistor switch a higher current from an external source (Collector) towards your load (Emitter).