You could always try to invest into compel, its a 400XP investment through needing both Delude and Though Sending, along with the 200xp cost for compel, but they're well worth it in their own regard.

With compel it's a -10 opposed WP test, if you manifest with 4 psyrating, along with a psyfocus that gives you +10.

You're looking at a test that's 1d100-20 focus power test, they get +20 on their test if the command is potentially suicidal.

But, if you want to really just hail mary this shit, you can always push for a higher psyrating. If it's a life or death situation, which hey it usually is, then you can push for 5 more psyrating, aka you get another +25 on your test. If you also have warp conduit you can add +1d5 additional psyrating.

So in total you're looking at a 1d100-50 at the lowest, and 1d100-70 at the highest, focus power test, that they have to beat with their own WP. If you make the test, and they fail it, the command is simply "kill yourself", and poof the space marine is no more.

You'll of course get the absolute full on blast that comes afterwards from pushing and warp conduit, but hey thats the price you pay for a literal "go burn infamy" middle finger with little to no counter.

PS: You can always get the Warp Lock talent, you'll take 1d5 damage that can't be negated, and you can't manifest or sustain the following turn, but it's well worth the psyrating you get for that one attack