I am developing an animation based on rhino render, but when Bongo controls the rhino-render application, it keeps on building it on-screen. Is there a possibility to avoid this? (and only render/store the individual images, not show them?)
Is there any specific reason why you don’t want the renderings to show?
You can simply minimize Bongo’s render dialog to get on with another computer-job, but you’ll find it a disappointing experience because the rendering weighs heavy on the CPU (often 100%).
You can better do some gardening meanwhile 
I would like to improve render-time :). But I’ll concentrate on my garden in the mean time.
Thank you! 
It won’t really make a lot of difference to render time - and the disadvantage is that you won’t be able to see if what you’re producing is any good.
Here’s my animation render tip:
Do a test of three STILL frames first: one from the beginning, middle, and end sections. This will usually be enough to avoid surprises.
Otherwise, you may find out that the lighting stinks in the second half of the sequence… and then you have to do the whole thing over. This test will catch any problems and let you fix them before you spend so much time waiting.