ignore I should LTR - Semi tone, not tempo.... my bad i'll leave the comment strikedthrough in case its info someone may find useful.
slap me with a wet fish.
VST host option, send to external .... nah, doesn't really address the request though if you're wanting to adjust & audition in realtime per audio clip/sample.
Seems bad form to suggest an alternate app.
Apologises first if this is not what you're after or have considered and not been satisfactory but can it not be done with a toolbar option?
Right click the "Configure Toolbar" and add the options (listed below) and assign a png icon for the button(s) of your choice for a silouette icon set such as IconMoon's.
As I understand there' s 5 tempo options:-
2 each for increase/decrease by 10% +/-,
1 for setting a preset, called "Set",
1 to "Use" said preset
& lastly another to "Reset".
It's alphabetically in the "Player" group in the pulldown menu in the "Set Toolbar Buttons".
Again apologise if [not if, you did]
I've just told you what you know already.