Yep, so many options.

1. Shikamaru catches Sakura on her way to work at the hospital and they walk and talk on the way. Ino manages to catch Shikamaru and Sakura from the window?

2. Sakura is heading home after a long day of physical training and medical training, Shikamaru could be waiting outside the hospital or by her home.

3. It's the weekend, she's off and Ino is working, thus a perfect time to pay Sakura a visit, gets suckered into staying over for lunch or something.

Choices choices...thoughts? On one hand, Ino spotting them now wouldn't be too weird, it might be what Shikamaru wants, to kinda drive Ino crazy. Or he wants it to be seriously established in secret and to have Ino find out after the fact they're now dating.