It's actually possible, if you do it correctly, but this probably breaks the game in the future releases (because the flags for Lisa and Olivia become quite messed up afterwards). The base setup as follows:
1. Start mentoring opportunity.
2. Start Olivia branch.
3. Continue mentoring opportunity, stop right before the final step of allowing you to become Lisa's boyfriend. Don't invite Olivia over to your pool before this.
4. Finish Olivia branch.
Here's where the mod's character flag menus comes in. You need to manually increase the level of Lisa's opportunity to its max (from 20/21 to 21/21 if I recall correctly). If you increase the flag with more than 1, the game will not allow you to have both branches active. If you decrease first and the increase, it will not work (dunno why, probably some other flag being activated that is not shown in the mod menu). When you have increased the flag by 1, you'll be able to ask Lisa to become her boyfriend. This starts the nighttime mentoring lessons with Kira, which you finish normally. Afterwards, you're still able to have Olivia over with sleeping pills whilst still having full benefits of being Lisa's girlfriend.
As previously stated, Lisa's and Olivia's flags become really messed up in the process. I cannot even look at Olivia's flags in the Cheat Menu without the Cheat Menu automatically closing, and for some reason, Lisa's flags are shown almost as resetted. If I manually change any of Lisa's flags in any direction, the game becomes screwed up and will not let me be her boyfriend anymore. Other than that, everything works normally.
Because this method will likely break the game in the future releases due to flag issues, you probably should take a copy of your savefile before you manually change the character flags.
) u can see the script with one "extract"
