With the chip you are using, the ADC is either configured with 10 bits or 12 bits resolution. It is not a common practice to switch the ADC mode back and forth between these two resolutions. You might still give it a try and integrate your own C code with the C function call block, but I would not advise to go that way as I am not convinced it can work (as mentioned in previous post, there are delay to respect etc…).
With the ADC set in 10 bits, you have up to 4 sample and hold channels which can run in parallel. Typically, channels 2,3 and 4 are used to sample motors current and voltage in sync with the driving PWM signal. Channel 1 is used to scan as many analog inputs as required, taking a different input at each new sampling trig. But you could also use this channel 1 to oversample your sensor and obtain a higher resolution thanks to dithering effect.
Another solution is to use an external component working over SPI or I2C. The blockset provide SPI and I2C blocks capable to connect any sensors using theses protocol. Blocks handle the I2C/SPI protocol in background which minimize the CPU load allowed to theses tasks. Microchip propose many ADC components (please visit: http://www.microchip.com/...g-to-digital-converter
); some of which are optimized for instrumentation. I have been using MPC3425 and MCP3428 (which include an instrumentation amplifier with programmable gain and output a 16 bits value) and could share further information if you are interested-in. Last, theses components are easy to solder as they require just few extra capacitors.
The multitasking monotonic rate scheduler implemented by default with multirate model make it very easy to keep a fast motor control algorithm (~20khz) running while having a slower (1khz ?) task dedicated for instrumentation. It allows keeping synchronized motor control algorithms output data (debug) with instrumentation data which might be important when analyzing data.