Manually add new ads to a playback

I'm developing custom ad playing feature for an app and already implemented IMA SDK-like functionality (a pre-known set of ad breakpoints and playing ads on these breakpoints).

This working ok, but when we tested it on production (3000+ DAU) we faced on some technical difficulties in expanding and optimizing functionality:

1. the biggest problem is that the advertising points are rigidly fixed on the timeline, which creates many technical and ideological difficulties when, for example, the user rewinds the content forward and backward. (the user can easily skip over an advertising point and it has to be skipped (since, for example, it has not yet been loaded into the player and the user does not have to wait for it to load in real time) - the idea is that the internal logic of the application can load an ad in the background and insert it in real time at any place on the timeline immediately

2. the other problem is about "Interval midrolls" - the main idea is not to tie advertising to specific points on the timeline, but to track the time the user spends watching content (for example, 10 minutes, no matter where he rewinds) and at the right moment insert advertising immediately at the current position of the player

The main question - is it possible to implement in latest media3 lib in any way?
P.s no, we can't use 2 player instances in our app due to hard technicals limitations
P.p.s there are no public guides or manuals about whole build-in ads feature in media3