This one was a bit of a mind bender but I think I have an idea of what you’re looking for. Essentially what you’re looking to do is change the seek speed based on parameter. This is not possible as of the date of this post and would make a great feature request. So instead you’ll have use the timeline in order for you control how long you want your transitions to be.
I’ve attached a picture to give you a better idea of what I’ve done:
As you see, you’ll need to do all permutations of param==>param and vice versa. Although this is cumbersome, you do save your programmer from making this (even though it might be faster for them to do it :S) and also you have complete control over the length of transition from one param to another while making multiple automation changes. Notice in the Transition Timeline I didn’t specify what the automation line should do. It will automatically do it for you by default. If you want, you can make it go crazy for the specified amount of time. In the example photo I posted, I made it 5 seconds as per your spec. If you still need help with this, send me a message and I’ll send you the project file that I made.