Heres how I do it, i might find a better version soon, but this is what we got right now.
my strategy is,
find a customizable brick.
screenshot its UV map
go to google drawings
draw what sticker you want in the UV map
screenshot that.
put your screenshot as "colour" in the sticker menu.
(Multiple screenshots might be taken to be able to get the right size)
create and title sticker.
done!
No downloading anything!
when you are done, you can delete the screenshots that you didn't use!

hopefully this is a bit easier.