You will be able to do it after the second half of June.
https://developers.line.biz/en/news/2020/05/20/liff-endpoint-url-improvement/
My LIFF endpoint is https://gang-nam-line-bot.herokuapp.com/liff/drawing-board
With params in LIFF url https://liff.line.me/1654307795-myblyO81/?key=test
It will redirect me to https://gang-nam-line-bot.herokuapp.com/?key=test
You will be able to do it after the second half of June.
https://developers.line.biz/en/news/2020/05/20/liff-endpoint-url-improvement/