What you plan to do is called bit banging an i2c port. I can't personally recommend doing this because there are a lot of variables involved in getting it right and there is a much easier workaround if you are willing to add hardware.
What will be much easier is muxing your i2c port with your SPI1. To do this you'll need a switch (even a DIP switch will work) or i2c expander to connect/disconnect the i2c clock and data lines entirely via GPIO. On the other side of the switch attach your i2c devices.
In the makefile add:
APP_PATCHES_AND_LIBS += enable_spiffy1_i2c_interop.a
APP_PATCHES_AND_LIBS += a4wp_hal_api.a
And in your .c file import:
And in your create function call:
Then in your create function (following boot from SFLASH) toggle the Chip select GPIO of the SFLASH to turn it off, then the GPIO of the i2c switch to turn it on. You can now carry out i2c communication as if nothing was ever changed.
This i2c switch will be a feature of the new development board to be released in the future.
It's great, and we will try to test with your suggestion.