In the section on the Multiple Attack maneuver, 6e2 p77 gives us a hint as follows:
COMBAT SKILL LEVELS
Unless the GM rules otherwise, characters cannot buy Combat Skill Levels specifically with Multiple Attack. They have to buy CSLs with the attacks they use to make a Multiple Attack, which they may apply when making the Multiple Attack with those attacks.
Thus, by my way of thinking, if you can't buy Combat Skill Levels specifically with Multiple Attack, you also logically shouldn't be able to buy Penalty Skill Levels specifically with Multiple Attack. Instead, I would think you would need to buy Penalty Skill Levels with the attacks used to make a Multiple Attack -- which could be applied when making the Multiple Attack with those attacks. This would make the PSL purchase approach congruent/consistent with the CSL purchase approach outlined above in the quoted RAW.
With that in mind, someone who has a DCV of 6 and a Blast, RKA, and TK (small group of attacks) with which s/he wants to Multiple Attack ... and not suffer halved DCV might purchase the following (which dodges the PSL question, entirely -- that being my point):
+3 with a small group of attacks (9 Active Points); Limited Power: Only usable during a Multiple Attack (Power loses about half of its effectiveness; -1), Limited Power: DCV Only - Cannot be used for OCV or to add to DMG (Power loses about half of its effectiveness; -1)
Different people might give different values for the limited power modifiers, but I think I've been a bit conservative, here, as technically the DCV-only limitation constitutes 2/3 of the power's effectiveness going out the window, right there. (i.e. Of the 3 things you can do with the CSLs, two thirds of them are off the table - yet I only listed this as losing half its effectiveness.)
The player must still state use of these levels for the Multiple Attack ... even though it's the only time they are usable. That's RAW for CSL's ... i.e. they are NOT persistent and a player may not state they are in use 'at all times' -- per 6e1 p69. These CSLs would also be for only ranged attacks ... since the powers being affected by the CSL are ranged powers and if they could affect OCV for those powers (i.e. no DCV-only limitation) it would be ranged OCV. (This is also per 6e1 p69.)
Check out the first paragraph of 6e1 p70 -- especially the last sentence of that paragraph ... for how to properly buy CSLs with limitations ... that affect DCV for both HTH and Ranged attacks; it's a lot more expensive ... and for a good reason!