Here's the idea:

Daily Detail

The whole trip occupies about 32 days for Chris, 23 days for Kathi.
Kathi and Chris are together for 20 of the 23 days.
After Kathi heads home from Helsinki, Chris rides 8 more days, hangs out with Joe & Bridget before heading home.
  1. Fly PDX→AMS (Chris & Kathi)
  2. Fly AMS→ZUR, ZUR→Zug (Chris)
  3. Ride Zug→Frankfurt 5h15m 428km
  4. Ride Frankfurt→Amsterdam 4h20m 441km
  5. tourist CU&KB in Amsterdam
  6. Amsterdam→Hamburg 4h28m 464km or by 5h8m train
  7. tourist CU&KB in Hamburg
  8. Hamburg→Copenhagen 4h36m 338km
  9. tourist CU&KB in Copenhagen
  10. tourist CU&KB in Copenhagen
  11. Copenhagen→Oslo (Kathi flys 1h10m, Chris drives 6h30m 600km)
  12. tourist CU&KB in Oslo
  13. Rent car, drive Oslo→Stavanger 6h47m 548km
  14. drive Stavanger→Bergen 4h34m 207km
  15. drive Bergen→Oslo 7h47m 518km
  16. Oslo→Stockholm 6h3m 522km while Kathi Flys 55m or takes the N600 train for 7h5m
  17. tourist CU&KB in Stockholm
  18. tourist CU&KB in Stockholm
  19. Stockholm→Umeå, Sweden 7h 637km, while Kathi flys to Helsinki
  20. Umeå, Sweden→Helsinki 9h28m 540km (includes 4h45m + 4hr ferry ride)
  21. tourist CU&KB in Helsinki
  22. tourist CU&KB in Helsinki
  23. Kathi flys home to PDX while Chris rides 5 days to Zug, first day ferry→Talinn, Estonia 3h10m 87km
  24. Talinn→Riga, Latvia 5h12m 392km
  25. Riga→Vilnius, Lithuania 4h37m 304km
  26. Vilnius→Warsaw, Poland 6h51m 427km
  27. Warsaw→Wrocław 5h30m 349km
  28. Wroclaw→Dresden, Germany 4h26m 262km
  29. Dresden→Stuttgart, 8h32m 517km
  30. Stuttgart→Zug, 4h19m 256km
  31. Hang out with Joe
  32. Zug→ZUR→AMS→PDX