ToPi

TS stated that using CS to alternate isn't possible (for some obscure reason), but he didn't state that absolute parallelism is required. I think you can write to one SPI port without it affecting anything else, but the code to communicate with the SPI peripheral itself takes some cycles.

The g2553 has 2 spi ports. I don't think it's possible to use any them absolutely simultaneously though. There will always be a minimal but countable cycle delay. Just figure out if it is faster to R/W to different ports or to just use different CS pins.

Except for the MSP430G2955 or MSP430F... the usual launchpad chips do not support more than one SPI port at once. This limitation can be overcome by using software SPI, I guess there are people who made a library for this, since SPI isn't that complicated at all.
If you fail to find one, I can write one up for you if required, though I'd like to know how timing etc. should be handled in this case.