The older calculators (i.e. everything older than the 9860 series with OS version < 2.00) don't have string variables, that much is correct. However, you can use the Locate command to print text anywhere on the display. With that you can just print the pieces of your string one by one, like this:
"Value of A"?->A
I hope I got the coordinates right... I don't have a Casio calc with me, and I haven't used one in a looong time (HP calcs are so awesome once you understand how they work). Anyway, the 3 and 2 specify where the last parameter (A in this case) is printed. The last parameter can be a literal string (in quotes) or anything that evaluates to a number (in that case the number should be printed).
Note that the autoscroll feature of the other text-related commands (text in quotes, ?, the little triangle ... did I miss one?) may screw with your carefully calculated Locate coordinates. What I usually did was filling the display with seven times " " at the start of the program and after any use of ClrText, so any further use of these commands would be guaranteed to scroll the display. Then I'd be able to write to the display with Locate, scroll it with another " ", and use ? and the triangle without them overwriting one of my Locate lines.
Another useful fact: on these old machines text simply put into quotes is printed very slowly (you can watch it appear letter by letter), but Locate with the same text is much faster. The downside is that Locate cannot scroll, and it cannot wrap long lines either. My usual trick was to use " " to scroll the display (just one space, that's fast enough), then Locate 1,7,"My long text here" which immediately overwrites that space I printed.
If you find that 7 lines with 21 characters each is not enough space for your text, you can also use the graphics display instead (it uses a smaller font for text). The command to print text there is named Text; like Locate it can deal with literal strings (with quotes, as usual) and anything resulting in a number, and it takes pixel coordinates (1,1 for top left corner; warning - the parameters are swapped compared to Locate). You can also decorate that text with F-Line and the PlotOn/PlotOff, PxlOn/PxlOff commands, but it's impossible to scroll the graphics display without erasing all text and decorations. Input is also limited as you can use Getkey to read the keyboard directly and react to that yourself, or you can use the Plot command combined with the small triangle to let the user move a cursor (the key turns the pixel at the cursor location on and stores the coordinates to X and Y).