I'm pretty sure cyndaquil does it with the four heads of his copulatory organ. Arbok and the other snakes do it with their hemi-copulatory organ most of which has two heads. Tentacool, Octillery, Tangela and Jellicent employ tentacle play. Torchic, Combusken and Blaziken do it real quick because they're chickens. Delcatty probably uses barbs to make sure it scrapes out some other male's sperm. Farfetch'd, Psyduck, Golduck and Ducklett have this incredibly long corkscrew copulatory organ which they use to penetrate Ditto.
Step 1: Put ditto on bed. Step 2: Take your clothes off. Step 3: Walk towards it. Step 4: Let it wrap all around you. Step 5: Wait until you do your thing. Step 6: Clean up if necessary. Step 7: Go to sleep in the other room. Step 8: Wake up and see an egg. Step 9: Congrats. You're now a dad. Step 10: Enjoy your baby.