Are there any good options other than filling the trem cavity, using a block, using extra springs, etc? I'd like a permanently converted hardtail bridge from my am standard strat.
In a word - no, at least that I know of.
The hardtail has a distinct sound that is not for everybody. If you like the sound of your guitar, the two most-used solution (block and/or 5 springs tightened fully) is really the way to go.
The only way I would imagine to be the "right" way to convert a trem-style Strat to hardtail would involve considerably more work than would be realistic, at least imo. The Trem-o-no is a nice option as well, come to think of it...
..try a hardtail, and if you like the sound, buy one!