Tried taking the excellent tutorial by bearsoundz [1] a tiny bit further. This uses the basic triple oscillator and builds in some mild effects to try to emulate several orchestral strings playing together. I feel like many string presets have a bit too much de-tuning and so this intentionally has less. You can tweak to your liking. Try adding multiple tracks and playing with each track's PAN and PITCH to get a more full-sounding string section in your "orchestra."

https://www.youtube.com/watch?v=3JZlUQuawNU

[1] LMMS Tutorial: Building a String Preset, https://www.youtube.com/watch?v=4hmJYW14JpU
[2] Some inspiration for you: https://www.youtube.com/watch?v=QYu2XgKYUYs