How to properly convert .ass to .sup with overlapping timestamped subtitle?

[leml]

I have an .ass subtitle file. It has two styles, one for dialogue and one for song lyrics.
The dialogue subtitles are displayed at the bottom of the screen and lyrics for songs are displayed on the top of the screen (toptitle).

I have converted this .ass file into a PGS (.sup) file using Subtitle Edit. However, I run into a problem where if the dialogue subtitle and the lyric toptitle have overlapping timestamps, only one of them is displayed. My understanding is that this is due to Blu-ray players can only display one PGS image at a time.

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For example:
line 1, Dialogue, 00:01:02 - 00:01:70 Hello
line 2, Song, 00:01:50 - 00:02:80 This is song lyric

After converting to .sup, even though both lines are converted, when playing the video, only the first line would display and the second line is not displayed on top.
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I have already tried numerous workarounds that failed:
1. Use easySUP for conversion instead: Failed. easySUP does not run on my PC, the cmd.exe window flashes for half a second and no .sup file is generated.
2. Use SupViewer to combine two .sup file: Failed, SupViewer errors out when importing the .sup file with error related to "SUP signature".
3. Mark the lyrics subtitle lines as "Forced" during Subtitle Edit conversion: Failed, does not resolve the issue.

Is there a way to convert .ass to PGS(.sup) file so that overlapping subtitle lines are generated into one image instead of two images? This should be possible given anime blurays often have a "forced" sub-track that only display subtitle for "Signs & Songs".

[leml]

Here is an example on the ideal output:

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Example .ass subtitle with Dialogue as subtitle and Song as toptitle:

line 1, Dialogue, 00:01:02 - 00:01:70 Hello
line 2, Song, 00:01:50 - 00:02:80 This is song lyric
line3, Dialogue, 00:02:17 - 00:02:92 World

after running conversion to SUP, the ideal output would be:

SUP frame 1: 00:01:02 - 00:01:49 Hello (subtitle)
SUP frame 2: 00:01:50 - 00:01:70 Hello (subtitle) This is song lyric (toptitle)
SUP frame 3: 00:01:71 - 00:02:16 This is song lyric (toptitle)
SUP frame 4: 00:02:17 - 00:02:80 World (subtitle) This is song lyric (toptitle)
SUP frame 5: 00:02:81 - 00:02:92 World (subtitle)

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After searching the forum, it appears SupViewer can merge two SUP files to achieve this. However, as mentioned above, trying to load a SUP file generated by Subtitle Edit gives a pop error "Error: No SUP Signature Found". Given SupViewer is really old, there must be another software that can combine SUP right....?

[videobruger]

For EasySUP do you have Java installed?

[leml]

For EasySUP do you have Java installed?

Yes, I have Java installed given I can run BDSup2Sub no problem.