It's likely that any amount of potential would all get distilled down to the reality that there isn't much in this world that Clark likes more than just Bruce's hands on him. Which doesn't mean it's not fun to deviate, to play with being denied exactly that, but part of what makes the red sun lamp as appealing as it is is the intensity of contact, giving and getting.

He groans out loud when Bruce pushes his fingers in without pause, and again when again. He's already slowly winding up the reins on self-control, a grip that once again threatens the longterm integrity of the nice sheets he's on in a fist, when he recognises the patience and deliberation on Bruce's half.

Instruction contrarily encourages the opposite, a warning pulse of arousal.

There is a breathed okay out of Clark, half-muffled against the bedding. The added sensory layer of overworked skin, sore muscle, nerves on fire, all hum together, discomfort and pleasure itching the same scratch. Probably because of careful treatment than in spite of it, but this doesn't prevent Clark from shifting enough to lift his hips a little off the bed, slightly too beyond the point of being self-conscious.

The next deliberate, probing push against that spot get another groan, another 'Bruce', breathed out, a complaint that isn't.