I got 3 per-win IP boosts. They do not expire over time but every time I play a match it automatically uses one. Is there any way to switch to manually use IP boosts or disable it? (OK. I know. It's unusual to not use an IP boost. But that's not the focus.)
Unfortunately right now there is no method of disabling a per-win IP boost. If you're just playing ranked and normal games on Summoners Rift you shouldn't be too worried but if you usually play any other game mode there is a difference in the IP gain.
Per-win IP boosts do not have an expiration date as you've noticed but there also isn't really a point in delaying them if you play on Summoners Rift (The IP Gains will remain the same all the time there). Now if want to get the most out of the boosts you should play summoners rift normal or ranked games. Note that per-win boosts are only consumed after a win. Losing a game will not consume them.
So basically: You cannot delay the usage of the boost, you can however only play Summoners Rift to get the most out of it. If you're already playing this game mode you shouldn't be too worried.
I have the same problem, I don't have a lot of time currently and I used play a bot game everyday for the win of the day (it's fast and you win almost every game)
Now I got 4 free IP/Win boosts and I didn't want to waste them on botgames, because the boost would only give you ~25 extra IP whereas a ranked win gives you ~100 extra IP.
I looked for a solution but found none.