Hi,
i have seen i2c chips going nuts because some probing actually affected the chips state. So i fully agree with Jean here.
I2C just isn't meant to be used for hot plugging. And so isn't the i2c-tiny-usb. It's more a hacking and testing device and is e.g. very convenient to test i2c client drivers or to test some new i2c hardware. But i have never had a need for this before user land was available. And once it is you can really do any magic you want using e.g. udev and sysfs.
Also if you really need some chip to be available at boot time, then usb isn't for you. Usb can take pretty long to enumerate etc and you can never be sure when exactly a device shows up on the usb bus. You'd thus additionally need some means of blocking the entire boot process if you want to enforce that. E.g. the kernel can wait for boot disks to appear for exactly this reason. But it wouldn't make much sense to delay the boot for less cruicial things. Boot time is a critical thing and only the most important things are supposed to have a negative impact on that.
If you wan't an i2c device to be available at boot time, then you might consider to connect it to some non-volatile i2c bus. I am pretty sure the raspberry pi has one.