No. It is not possible to use the I2C bootloader in master mode to read flash data from an external device. PSoC I2C Bootloader is essentially an I2C Slave device that receives flash data from an external I2C master and updates the flash. Apart from the boot loading functionality this module can be used for I2C slave functionality in the application as well. But the module lacks I2C Master functionality. If the bootloader has to read flash data from external device and then update its own flash, this will require major modification of the BootLdrI2C user module code.
If the application requires I2C Master functionality during the application then I2Cm UM can be used.