How to break up C-Functions without increasing stacksize - c

Question

Working in embedded Systems design, I am often confronted with Legacy Code, where somebody wrote some ISR which consists of a huge if/else-Jungle, sometimes spanning multiple screen-lengths. Now, trying to be a good programmer I try to refactor the function, using the paradigms I learned, one of them being: "A function should do one thing only".
So I break down the function into multiple static sub-function, which have descriptive names and encapsulate variables. But since I am working on an embedded device, I need to be considerate of stacksize and the number of jumps (especially in an ISR that might get called often and might itself get interrupted by something else).
Now, of cause most(or even all) Compilers can be forced to inline a function (as __always_inline does with gcc). But even that increases stacksize, if I have to pass parameters (they do not necessarily get optimized away), even if it is just a few bytes per parameter.
Now for my actual question: Is there a way not to increase stacksize while breaking up functions in C?
EDIT:
To make my Question clearer: Here is an Example of some Code, where I just shifted some of the code to inline-functions.
Static stack usage is 144 without inline-functions and 160 with inline functions.
Original:
#include <stdio.h>
#include <string.h>
int main(){
char inputString[100];
scanf("%s",inputString);
static char delimiterArray[] = {' ','+','-','/','*','='};
for(int i = 0; i<sizeof(inputString); i++){
printf("%c",inputString[i]);
char* inputChar = inputString + i;
for(int j = 0; j<sizeof(delimiterArray);j++){
if( *inputChar == delimiterArray[j]){
printf("DELIMITER: %c",delimiterArray[j]);
}
if(inputString[i] == '\0'){
printf("\nNuberOfChars: %d\n",i);
break;
}
}
}
return 0;
}
With inline-functions:
#include <stdio.h>
#include <string.h>
static inline void checkForDelimiters(char* inputChar)__attribute__((always_inline));
static inline void decomposeString(char* inputString)__attribute__((always_inline));
int main(){
char inputString[100];
scanf("%s",inputString);
decomposeString(inputString);
return 0;
}
static void checkForDelimiters(char* inputChar){
static char delimiterArray[] = {' ','+','-','/','*','='};
for(int j = 0; j<sizeof(delimiterArray);j++){
if(*inputChar == delimiterArray[j]){
printf("DELIMITER: %c",delimiterArray[j]);
}
}
}
static void decomposeString(char* inputString){
for(int i = 0; i<sizeof(inputString); i++){
printf("%c",inputString[i]);
checkForDelimiters(inputString+i);
if(inputString[i] == '\0'){
printf("\nNuberOfChars: %d\n",i);
break;
}
}
}