Nice try! There seems to be less personal developements than usually... ;)
 
Yet I think you still could stick closer to the text (since you don't care for rhythm nor rhymes), for example :
 
If you only knew, how much fire,
How much life was wasted in vain,
 
And how much heroic fervor
For an uncertain shade, for a whisper (rustle)...
And how it turned my heart to ashes,
This gunpowder useless consumed
 
Сколько темной и грозной тоски > How much dark and bitter grief ?
 
(And where is the vokzal?)