There's not a single workaround for making libraries work- some of them don't compile as they use some avr-specific header files (which won't compile for Galileo because, as you correctly pointed out, it's an x86 architecture).
Now, sometimes there IS an easy workaround- for example in some cases the only AVR-specific header file used is <avr/pgmspace.h>, and if this is the case then often you can port it for Galileo without too much hassle, by removing any parts which store values in program memory and replace them with the standard C++ way for assigning/initialising variables.
Can you link to the library? I could be more helpful if you show me the library.
This library routine is extremely timing dependent. Your best chance is to put a note on Adafruit's support site and request a Galileo version.
Looking at the schematic, IO2 and IO3 looks the most promising since they're routed directly to the Quark processor.
All other IOs are routed to the CY8C9540A through a 100KHz I2C bus, severely limiting their io rate.
An alternative would be slapping another Audino CPU on top and use the Galileo to drive the IP stack.
One example could be http://www.cypress.com/?rid=77780 which you could get for 25$.
Sorry for the shameless advert. I'm not affiliated with Cypress, but I do love their IDE for developing with the PSoCs.