If you are having trouble with trying to get spies into structures over the internet with a human player you should try this:
1. Get two IFV's.
2. Get one spy.
3. Get one Tanya.
4. Change the spy's Identity to a Conscript or something that the enemy has around his base for defense.
5. Then put the tanya in one IFV and the Spy in the other IFV.
6. Send them at there base.
7. When the tanya IFV is under attack sneak the other one next to a structure(Barracks, War Factory, etc.)
8. Tell the tanya one to attack the structure that the Spy IFV is next to.
9. Tanya's will blow up and the spy one will too but the spy will come out with a disguise. The player will be too busy to notice that that Conscript or unit is not theirs and you will not have any problem sneaking it into that building.