PSLV in Fidelity brokerage account - is there a way to sell without incurring tax on the gain?

I have some positions in PSLV (less than 6 months old). I don't want to cash out permanently but I do want to sell a portion of my PSLV and with the proceeds increase my position in other assets in the same brokerage account. Is there a way to do this without there being a taxable event? Can I somehow defer, or simply "exchange" PSLV for another asset without tax implications?