ATMEGA328P: Can I re-use PB4(MISO) w/ a pull-up resistor w/o interfering w/ SPI?
It would be extremely easy to provide a pullup that was active only during initialisation and that "vanished" completely thereafter.


Active: PNP transistor is turned on by a capacitor at powerup and pulls pullup high. Cap is charged and transistor trns off after 1 to 2 time constants.
Passive: Capacitor provide V+for pullup resistor via a diode. Cap charges (or effectively discharges depending on perspective) with a separate resistor and pullup drive disappears aftr 1 time constant or so. Diode makes cap "invisible" when "charged". 




(1) An "active pullup" would be easier to "design" properly than a passive  and could consist of a capacitor and a "digital" transistor (ie internal base resistors). So could be very small - two components plus actual pullup resistor. Adding another r or 2 may help get timing more predictable but 1R version should be OK.


Digital PNP with internal R from  base to emitter and internal R  from base to base input pin. 
Capacitor base pin to ground.
Collector to pullup.


On turn on Vcap = 0 so base input pin is at 0 so transistor is on.
 Cap charges via internal base resistor.
 When Cap reaches ~= V+ -0.5 transistor turns off. 

Size /cost / values: See (2) below for capacitor sizing and cost, but note that a much smaller capacitor value may be used by choosing  a much larger base resistor value to charge the capacitor  than can be used with the passive design. eg a 10k base resistor would allow about a 1 uF cap and something as extreme as this ROHM PNP with 100k input resistor datasheet here would allow probably a 0.01 - 0.05 uF range cap.  Available in 4 pkgs from SOT23 down to VMT3 1.2mm x 0.8mm !!! :-) for the terminally enthused.   ).047 uF X5R cap can be 0201 (if desired) for equal amusement at under 1 cent 

Transistor cost dominates here in this case at about 10 cents !!! but much much cheaper will be available.  

(2) A passive pullup is probably larger and more costly as installation cost will predominate in volume manufacture. But:

This could "safely" be as little as 


C1 = 1 x cap (C+ = V+), 
R1 = 1 x resistor (C- to ground), 
D1 = 1 x diode (junction of R&amp;C to pullup), + 
R2 = pullup to wherever.


C1 starts with 0 charge so when V+ rises C+ is pulled to V+ and C- also. Cap now discharges via R1 so C-falls from V+ to ground. D1 isolates cap from pullup once cap is discharged. Pullup provides whatever value is required for bus. I2 R2 = pullup is say 5 to 10+ times as large as R1 then R1 will dominate discharge time. 

Size /cost / values: If you need "a few mS" say time constant = 10 mS. 
 Maxim say pulup should be about 4k7.
 This is shown the same for parasitic powering and when Vdd is available so I strongly suspect that a larger value is acceptable when Vdd is provided BUT lets stick wityh 4k7. (Other issues is time constant od R oullup +_ parasitic capacitance on 1 wire bus). 

Make R1 = 1k.
 Time constant = 10 mS
 so C1 = 10 uF = not nice, but bearable.

eg this TDK 0805 pkg, 10uF, 10V, Y5V material, costs 2.5 cents at 2000 volume and under 2 cents above 10k volume at Digikey. Probably half or less from China. Y5V may be a bit "exciting at say +20%/-80% across temperature (-55/+85) and still not marvellous at say 0-55C. 

Rather better X5R (+/- 20% across temperature) is also ins ame size pkg (0805 x 1.5mm tall) at about +50% price premium (Digikey 2.8C/26k) 

Given the horrific price of the 1 wire IC you may not mind the few cents for the cap. 

(3) PIC10F or similar drives pullup :-)

Or then there's this which I think may be a one off offer, or a mistake or last years April fools day joke or ... . 
  33 cents/10 k for microcontroller with 5 x 10 bit ADC, Brownout, power on reset, IIC, IRDA, SPI, UART, PWM, internal osc, watchdog, 8kB flash, 128 byte eprom, ... !!!!!!!!!!!!! datasheet.
 What a pullup controller that would make :-).