: Add your powder to a small amount of mixed epoxy, mix into a paste,
: add more epoxy to thin the paste, and so on until your mixture
: is ready to add to the epoxy batch.

: Ted

That is the route I'd go except that I would mix the powder into a paste of epoxy without the hardener mixed in, keep adding the measured epoxy, finally add the hardener. That will give you all the time you need to get a decent mix. Add the hardener last to avert the stress of haste.

It may also help to decant some epoxy resin and warm it in a bowl of hot water before you mix.

Et