Changing bit rate on SCI

I'm working on an application for the S7G2 that uses the SCI configured as 4 separate SPI ports.

My normal bitrate will be 6 Mhz. My external peripherals can handle this when writing data to them through MOSI.  However, when my device boots, I need to read some configuration data from my slaves devices through MISO. The slaves can not set up their MISO pins fast enough to support this rate, so I need to operate at a slower rate during initialization, then shift up to the faster 6 Mhz. 

I would like to start communications at 1 Mhz, then boost up to 6 Mhz.  Unfortunately, the bit rate variable in the spi

g_spi0.p_cfg->bitrate

is read only.

Is there any way to change bit rate at runtime, perhaps by using multiple configurations, of bit banging, or anything at all?