Sure, write the translation from whatever x,y are to the character form...it's not clear what they represent, however, but if they're character strings then all you're missing is the concatenation...
x='A';
y='B';
rnge=[x ':' y];
data=xlsread(FileName,rnge);
If they're numeric you'll have to use num2str or sprintf or similar to build an appropriate string but it can be anything that results in a valid range expression as a character string (a cellstr won't work).
