Shouldn't take much force to press them in. I just had my DME out yesterday and made a mental note of how 'clever' the little clips were. Untill you get it figured out, no worries about driving it without the clips in. Might want to stuff a sock in there in the mean time so it doesn't get bounced around too much. Sorry I can't provide any more insight, except of course, make sure they're being installed the right way round Come to think of it, another time I removed them, I had trouble pulling one out and had to bend it a bit to get it back in. Don't remember the details, but it had to be slightly bent to work.
Dave