Okay, it's messy. It can be done,but you're going to need somebody sympathetic at the airline to do it for you. Any T.A. that tries this technique may get a debit memo. I don't know either way.

The problem that I found was as Empress stated: when you build the itin sector by sector, the YEG-YVR sector comes up as Zip.

You book the first flight:
1 AC 123L 12NOV YYZYEG SS1 845A 1051A * TU

Now for YEG-YVR the next day, checking the availability in Galileo:
*** AIR CANADA ***
13NOV WED 1000 YEG - YVR VANCOUVER.BC.CA
1 YEG YVR 0645 0725 Y4 M4 B4 H4 V4 Q4 L4 N4 3J6241 737 0
2 YEG YVR 0900 0940 Y4 M4 B4 H4 V4 Q4 L4 N4 3J6243 737 0
3 YEG YVR 1010 1050 Y4 M4 B4 H4 V4 Q4 L4 N4 3J6245 737 0
4 YEG YVR 1145 1225 Y4 M4 B4 H4 V4 Q4 L4 N4 3J6249 737 0
5 YEG YVR 1500 1540 Y4 M4 B4 H4 V4 Q4 L4 N4 3J6251 737 0
6 YEG YVR 1630 1710 Y4 M4 B4 H4 V4 Q4 L4 N4 3J6253 737 0

They all have the 3J code on them.
Now we do a trick, we ask for YEG-YYJ, which of course, goes via our destination. Watch this:
*** AIR CANADA ***
13NOV WED 0700 YEG - YYJ VICTORIA.BC.CA NTE
1 YEG YVR 0645 0725 Y9 M9 B9 H9 V9 Q9 AC6241 737 0 963
L9 N9
2 YVR YYJ 0905 0930 Y9 M9 T1 B9 H9 V9 AC8055 DH3 0 959
Q9 L9 N1
3 YEG YVR 0900 0940 Y9 M9 B9 H9 V9 Q9 AC6243 737 0 963
L9 N9
4 YVR YYJ 1010 1035 Y9 M9 T1 B9 H9 V9 AC8413 DH3 0 959
Q9 L9 N1
NOTE 959 OPERATED BY/EXPLOITE PAR-QK/AIR CANADA JAZZ
NOTE 963 OPERATED BY/EXPLOITE PAR-ZIP
[This section truncated slightly.]

AC does not use marriage technology, so it is possible to book both and then cancel one.

2 AC6241N 13NOV YEGYVR SS1 645A 725A * WE
OPERATED BY ZIP DOMESTIC SVCE
3 AC8055N 13NOV YVRYYJ SS1 905A 930A * WE
OPERATED BY AIR CANADA JAZZ

Now cancelling the unnecessary sector and we have:
1 AC 123L 12NOV YYZYEG SS1 845A 1051A * TU
2 AC6241N 13NOV YEGYVR SS1 645A 725A * WE
OPERATED BY ZIP DOMESTIC SVCE
We add a return sector and autoprice:
1 AC 123L 12NOV YYZYEG SS1 845A 1051A * TU
2 AC6241N 13NOV YEGYVR SS1 645A 725A * WE
OPERATED BY ZIP DOMESTIC SVCE
3 AC1130Q 17NOV YVRYYZ SS1 1130A 649P * SU

*FARE GUARANTEED AT TICKET ISSUANCE*

E-TKT REQUIRED
*PENALTY APPLIES*
LAST DATE TO PURCHASE TICKET: 03OCT02
$B-1 C02OCT02-SITI
YTO AC YEA Q28.00 222.00LLECONO1 AC YVR Q28.00 94.00N7WOW AC
YTO Q28.00 319.50QLWCANAD CAD 719.50 END
FARE CAD 719.50 TAX 53.69XG TAX 25.00SQ TAX 22.43CA TOT CAD
820.62
So it can be done, kind of! It is exploiting a vulnerability in which Zip is obtainable as a codeshare ONLY AS PART OF A CONNECTION. But it is considered an illegal procedure.

Further note, that if the 3J code were booked that payment would not be allowed to wait until the next day, but would be required instantly.

Now travel agents are told that if the computer autoprices an itinerary that they [the GDS]will honour it.

There is no problem if we make YYJ the destination:
1 AC 123L 12NOV YYZYEG SS1 845A 1051A * TU
2 AC6243Q 13NOV YEGYVR SS1 900A 940A * WE
OPERATED BY ZIP DOMESTIC SVCE
3 AC8413Q 13NOV YVRYYJ SS1 1010A 1035A * WE
OPERATED BY AIR CANADA JAZZ
4 AC1190Q 17NOV YYJYYZ SS1 730A 255P * SU
*FARE GUARANTEED AT TICKET ISSUANCE*

E-TKT REQUIRED
*PENALTY APPLIES*
LAST DATE TO PURCHASE TICKET: 03OCT02
$B-1 C02OCT02-SITI
YTO AC YEA Q28.00 222.00LLECONO1 AC X/YVR AC YYJ Q28.00
109.00QECONO2 AC YTO Q28.00 339.50QLWCANAD CAD 754.50 END
FARE CAD 754.50 TAX 56.49XG TAX 30.00SQ TAX 22.43CA TOT CAD
863.42
The problem only exists if you are travelling between 2 Zip! sectors.