| Rel, what about something even simpler and more straightforward? just a suggestion to be fleshed out later!
If a character uses up all his healing surges he gets a [Wound] and unless someone Heals him (with an ability check or a ritual, most powers shouldn't work here) he simply regains half surges per day. a character can have multiple [Wound]s and each one has to be treated separately. multiple [Wound]s stack but any one beyond the first subtracts only one surge from the wounded total
kinda equivalent to your first suggestion, but half surges at full power is both easier to manage and actually looks more appropriate to me... when wounded you have less energy reserves to draw from, but your body draws at them with the same speed! | 
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