I suppose another way to do this would be to manually create a list where one col is the range for the tuned parameters and another col contains the training df(s), like so:
library(tibble)
tibble(param = seq(0, 1, 0.1),
data = list(as_tibble(mtcars)))
#> # A tibble: 11 x 2
#> param data
#> <dbl> <list>
#> 1 0 <tibble [32 x 11]>
#> 2 0.1 <tibble [32 x 11]>
#> 3 0.2 <tibble [32 x 11]>
#> 4 0.3 <tibble [32 x 11]>
#> 5 0.4 <tibble [32 x 11]>
#> 6 0.5 <tibble [32 x 11]>
#> 7 0.6 <tibble [32 x 11]>
#> 8 0.7 <tibble [32 x 11]>
#> 9 0.8 <tibble [32 x 11]>
#> 10 0.9 <tibble [32 x 11]>
#> 11 1 <tibble [32 x 11]>
Created on 2021-10-14 by the reprex package (v2.0.1)
But if you wanted more complex tuning grids, you'd have to set them up yourself, which doesn't use the full functionality of tune/dials.