R doesn't make it super easy to deal with the summary as a string. Here is an example of returning the summary as a single string, using some slightly less-than-elegant R code:
example_lm <- glm(.arg2 ~ as.factor(.arg1))
f <- capture.output(example_lm)
paste(f, collapse = '\n')
You might find some better examples from Stack Exchange.
If that doesn't produce the result you're looking for, could you post an example workbook? R questions are usually much easier to answer with the context of how the dashboard/worksheet is structured.