How to stop a slideshow and then start again where you left off?

I started watching a slideshow of a whole album of 700 pics (of my son being born), then stopped it at photo 300, and now it won't start up again where I left off.

This is because iphoto automatically selects which photo you arrive at. And it seems like if you select a photo or group of photos, the slideshow will ONLY play those.

Of course, if I select no photos, iphoto plays the whole album from the beginning, but I don't want this either. I simply want to pick up where I left off. Is there really no way to just let the album play from a specific slide without annoyingly selecting the ENTIRE remainder of the album (400 photos)?

This should not be as difficult or impossible as it appears to be...

Iphoto 9.6.1 on Yosemite