Can I drive MOSFET gate with an isolated voltage source?
Yes you can.  Here is one...

PCSA1-S5-S15-S (Power supply, 5V to isolated 15V)

http://www.digikey.com/product-detail/en/cui-inc/PCSA1-S5-S15-S/102-3948-ND/6181043

If you don't care about speed you can just turn the supply on and off.

If you care about speed one usually uses an isolated DC supply and an isolating gate driver.  Like this one...

MGJ2D051505SC (Power supply 5V to isolated +15V/-5V)

http://www.digikey.com/product-detail/en/murata-power-solutions-inc/MGJ2D051505SC/811-2998-5-ND/4840065

1EDI60N12AFXUMA1 (Isolated MOSFET driver)

http://www.infineon.com/dgdl/Infineon-1EDI60N12AF-DS-v02_00-EN.pdf?fileId=db3a3043427ac3e201428e5da08f372a

One key factor when choosing a supply for gate drive is to pick one with a very low input to output capacitance.  The MGJ2 series meets that criteria.