openxlsx::writeFormula rowwise - is there an efficient way to do this?

openxlsx functions to write formula seem to add formula columnwise only.

Is there an efficient way to write formula rowwise?

Working through a reproducible example to illustrate the issue:

df <- data.frame(a = 1:3,
                 b = 4:6,
                 c = 7:9)

# create workbook, worksheet and write data to worksheet
wb <- createWorkbook()
addWorksheet(wb, "Sheet 1")
writeData(wb, "Sheet 1", x = df)

#  formula to be added rowwise to cells A5:C5
f <- c("SUM(A2:A4)", "SUM(B2:B4)", "SUM(C2:C4)")

# Using the openxlsx function results in columnwise addition of the formula vector: 
writeFormula(wb, sheet = 1, x = f, startCol = 1, startRow = 5)

saveWorkbook(wb, "rowwise_writeFormula.xlsx", overwrite = TRUE)

This results in:

writeFormula rowwise

The naive approach is to add each formula individually, maybe OK for small data sets.

writeFormula(wb, sheet = 1, x = "SUM(A2:A4)", startCol = 1, startRow = 5)
writeFormula(wb, sheet = 1, x = "SUM(B2:B4)", startCol = 2, startRow = 5)
writeFormula(wb, sheet = 1, x = "SUM(B2:B4)", startCol = 3, startRow = 5)

This provides what I want but is not a viable approach for hundreds of columns.

Using purrr::pwalk this can be wrapped up in a function, which is an improvement:

formula_inputs <- list(formula = f,
                       start_col = 1:3,
                       start_row = rep(5, 3))

purrr::pwalk(formula_inputs, function(formula, start_col, start_row) writeFormula(wb, sheet = 1, x = formula, startCol = start_col, startRow = start_row))

Either way this does what is required:

My question: is there a better way to do this? or might it be an enhancement to openxlsx?

In my real case I have 100 variables for 10 data frames in a list each requiring multiple (10) rowwise formula to build up to a total. In all about 10,000 formula need to be written, this takes several minutes; so any ideas on how to speed up the process would be welcome.

Note: openxlsx's alternative approach using writeData for vectors of class 'formula' also add the vectors as columns; when I try to transpose the vectors into rows the formula class is lost.