I don't think any I2C supports "turning the first bit off" simply because then the data stops being I2C. Either you write a custom bit-banging procedure which does something similar to I2C (you can even reuse some I2C code published somewhere) or if you want top use hardware I2C, you will have to use a hardware solution. Alternatively, if the target device is of a "smart" kind, you can send standard I2C and upon receiving remove the start bit in software (but if you could, why not implement standard full I2C instead?)
Being short on pins is not an excuse. Bit-banging could be implemented on the same pins. The excuse could be squeezing last cycles off the CPU (bit-banging DOES take some CPU time) or running out of internal resources like clocks, registers, scratchpad RAM etc. But if you don't have to abuse the I2C built-in hardware to generate non-I2C serial data, don't. Do it as it should be done: In software, from scratch.