I understood exactly what you were proposing, both the process and the expected results.
It appears that perhaps it was you that misunderstood my point.
Let's follow the logic...
The normal use of the product is to insert the straw into a gap, depress the trigger and fill the gap to ~50%. The foam will then expand and fill the gap.
Removing the product from the can, either forcibly or not, without the straw in the gap that you are trying to fill is pretty much a waste of time - and product.
So, do you really think that when the manufacture said "do not force the product from the can" that they were picturing consumers putting the can in a vice and carrying the vice and can to the gap and attempting to "force" the product from the can and into the gap?
If that's not what you are suggesting, then kindly explain the point of squeezing the can in a vice. Why would anyone "force" the product from the can if it wasn't to get the product into the gap?
If you really were planning on using the vice to force the product from the can and into the gap, then I'll say it again:
Let me know how that works out for you.