Hello! I have an '06 and I use cascading funnels to fill transmission fluid through the dipstick tube. I think I have 4 total, starting on the bigger size and getting sequentially smaller. The smallest one fits into the dipstick tube and is quite small. It actually came in a pack of colored sand for making sand art! The other funnels I bought from Dollar Tree.

Other options you could try are:
Aluminum foil - even double or triple thick -- that has been wrapped tightly around a sharpened pencil tip as a mold so that only a small hole for an opening remains. You could even place this at the end of the tube you already bought.
Aluminum pie tin -- lightly fold it in half and then half again and then carefully clip off a tiny opening at the pointy end, and then unfold it into a funnel shape.

To measure the dipstick tube's dimensions, you could take a small piece of foil and wrap it around the tip of the dipstick tube to make an impression and then measure the impression.

 

Thank you. Those are wonderful ideas--definitely have some foil around.

 

The transmission should have a fill plug, which may be a better choice to use.

 

but being an 04, there's a good chance it's got the flow jet recall fix installed in the fill plug hole.