batchtools_slurm futures block (Was: stdout/stderr to log file only when using slurm?)

I have a loop like this:
```r
for (i in 14:11) {
f <- future({
warning("Sleeping ", i, " seconds")
Sys.sleep(i)
saveRDS(i^2, paste0("tmp-data/res", i))
})
}
```
and I would to output the warning in the log files only.
I've seen the new option `split` in a blog post to do both (but I didn't find it in the documentation).
The problem is that capturing this output and returning it to the main session usually blocks my session for a long time (sometimes minutes), and I would like to avoid this.

Basically, is there any way to use future/future.batchtools just to submit jobs on a slurm cluster without returning anything to the session sending them?