First, my thanks to all who have read/considered my quandary. I appreciate your time.
As it happens, I have stumbled upon what may be sort of an answer to this riddle. If one summons the on-screen control buttons (I do this by pressing the "character space" key on the remote's keyboard), there's a bar across the top with five first-tier menu options. The second one from the left (viewer's left, right side of screen) has a classic "play" icon (filled ">"), and this yields an array of buttons at the bottom of the screen that starts with "PAUSE," then shows the two greyed-out skip options, followed by "REWIND, FAST FORWARD, STOP, PLAY." From here, there's no way to deploy the skip function, just frustration.
HOWEVER, looking again at the top-tier menu, there's one labeled "MISC" on the far right (screen's far left). When that one is selected, there is a comparatively small intermediate "radio" style bar, which can be toggled between left and right buttons. IF one selects the right (screen's left) button, the bottom array now shows five buttons--and the two on the left (screen's right) are "Instant Replay" and "Quick Skip." These are NOT greyed-out and operate essentially as skip forward and back instructions.
Needless to say, it's a bit tedious to get to these buttons, and the remote control itself has no built-in equivalent (at least not one I've found thus far). Also, as with any directive sent via SlingPlayer, there's a lag between pushing the button and effective communication of the signal to the STB, and efforts to send multiple skip messages in a cluster (rather than waiting for each directive to be implemented before issuing the next one) don't seem to work, so it's difficult/time-consuming to move back or ahead very far with these buttons. Thus, they are only a "sort-of" answer to the problem. Still, if anybody else is wrestling with targeted time-travel within recorded material, these rather obscure buttons may be somewhat helpful.