A possible solution is a ftable that contains
the numbers of the used instruments, for example

<CsoundSynthesizer>
<CsOptions>
-d -odac
</CsOptions>
<CsInstruments>
sr     = 44100
ksmps  = 64
nchnls = 1
0dbfs  = 1

ginstab ftgen 0, 0, 4, -2, 143, 221, 39

opcode turnoff_all, 0, ii
  imode, irelease xin
  ilen = ftlen(ginstab)
  kndx init 0
  if (kndx < ilen) then
    kinsno table kndx, ginstab
    turnoff2 kinsno, imode, irelease
  else
    turnoff
  endif
  kndx = kndx + 1
endop

instr 143, 221, 39
  kamp expsegr 0.001, 0.1, 0.2, p3-0.1, 0.2, 0.1, 0.001
  aout poscil3 kamp, p4, 1
  out aout
endin

instr stop
  turnoff_all 0, 1
endin
</CsInstruments>

<CsScore>
f1 0 8192 10 1
i143 0 36000 440
i221 1 36000 660
i39  2 36000 880
i "stop" 4 0.1
e
</CsScore>
</CsoundSynthesizer>

tito