Hi cksh.simon
People certainly automate EQ settings to make instruments stand out or fade into the background. It's really common for things like acoustic guitar in songs where in some places the acoustic guitar is prominent and in others it's not. More generally, the way to think about it is in terms of having the cello occupy it's own space. In music production the idea of "space" in an important one and can be handled in a few different ways. Here are some:
1. Frequency - this is what Beepster was talking about. When you remove some frequencies from other instruments you're carving out a space for whatever you'd like to be heard more. Removing overlapping or cluttered sounds makes instruments all have their own area to live in.
2. Depth. This is frequently accomplished with reverb or delay (which are really the same thing anyway...but I digress). Reverb gives the listener the illusion that an instrument is sitting back away from the them. To make an instrument more prominent remove some reverb.
3. Stereo field. This is the right to left axis in the stereo field. If each instrument has it's own place in the stereo field it will make them more intelligible and may require less tweaking to stand out in places where you want them to stand out.
4. Volume. Volume automation is EXTREMELY common in today's music and perhaps the easiest way to skin this cat. For the section where you want the cello to stand out bump up the volume a bit.
5. Time. Many good piano players will delay the melodic notes of a piano piece by just a bit so they don't fall exactly on the chordal, structural parts of the song. It's a really tiny amount so the listener doesn't interpret it as a mistake, but it can really make a difference. If you delay your cello part just a bit for the section you'd like to stand out it can separate it from the rest of the piece. Keep in mind it has to be a small amount or it will sound bad...just a few milliseconds.
These techniques frequently work best when used in combination. For example, if you have a section of music where you want the cello to stand out, try moving it's pan position a bit toward center, bumping it up a half db in volume, and removing just a bit of reverb. This gives the illusion that your cello player has moved toward the center of the stage and taken a few steps forward (if you watch jazz, bluegrass or vocal ensembles perform you can actually see performers do that exact thing).
Good luck
Dean