Dynamic naming of download filename from DataTable buttons extension in R shiny

I have:

library(shiny)
library(DT)

ui <- fluidPage(
    h2("Explorer"),

    tabPanel(h3("Inspector"),
             p("Overview of data for a particular sample."),
             selectInput(inputId = "sample",
                         label = h3("Select sample"),
                         selectize = TRUE,
                         choices = names(vcf_tibbles)),
             dataTableOutput("sample_inspector")
            )
    )

server <- function(input, output) {
  output$sample_inspector <- DT::renderDataTable(

      sammple_overview(sample_id = input$sample, vcf_tibbles = vcf_tibbles),
      rownames = FALSE,
      extensions = 'Buttons',
      options = list(paging = FALSE,
             dom = 'Bfrtip',
             buttons = list( list(extend = 'csv',   filename =  paste("snp", input$sample, sep = "-")),
                     list(extend = 'excel', filename =  paste("snp", input$sample, sep = "-"))))
      )
}

Everything works fine, in that I select a sample and the table correspondingly updates. And if I click CSV or Excel, the corresponding dta downloads. However, the file name is always wrong.

It seems that the content of the data table is being updated, but input$sample is not being considered with the buttons.

Is there a way to make the filename argument in the buttons also be reactive?

I tried to make the name be the result of a function call, but was unable to get that to work either.

Thanks!