Extract location of string in Excel sheet using readtable - excel

Question

I am writing a program that will use readtable to manipulate data that is read from an Excel spreadsheet such as the one below:
A B C D E F...
1 " " " " " "
2 " S 3 K3 " "
3 " " " " " "
4 " " 10 3C " "
5 " G 7 U " "
6 " " " " " "
.
.
.
I must extract the original location of some of the data, that is I need to store the location of 'S' as 'B2' and 'K3' as 'D2' etc. after they are read from the spreadsheet. To do this, I use readtableand then search for the location in the spreadsheet that contains the desired string; however, this requires that the entire spreadsheet be loaded into MATLAB.
I don't know in advance the number of empty rows or columns before 'S', nor do I know if some data will be filled in any of the columns in the rows above it. Additionally, I don't want the variable names to be generated automatically.
readtable('FilePath', 'ReadVariableNames', false, 'Range', 'myrange')
allows for not reading the variable names but doesn't allow for a dynamic range, i.e. the default option will skip the blank space and a specified range can't be dynamic.
opts=detectImportOptions('FilePath');
opts.DataRange='A1'
readtable('FilePath', opts, 'ReadVariableNames', false)
allows for specifying a start of the range but opts=detectImportOptions overwrites the 'ReadVariableNames' option, and the program reads the variable names anyway. The only workaround that I found was to use readtable without opts and to specify a range larger than the largest anticipated data set and then to trim empty rows and columns, but this is slow and clumsy. Is there a workaround?