This funnel allows for the compression and insertion of a tubeless tire valve stem from the outside of the rim when used together with https://www.thingiverse.com/thing:6058004 for ramming in of the stem. Use lots of silicone lube inside the funnel.

Print with 4 walls for strength.

As noted in the comments; this will be easier if you first dip the stem in boiling soapy water to soften it.